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EXPERIMENTS   WITH    PLANTS 


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EXPERIMENTS  WITH 
PLANTS 


W-.^jF  V.ioSTERHOUT,  Ph.D. 

ASSISTANT   PROFESSOR    OF    BOTANY    IN    HARVARD    rXIVERSITY 


EIGHTH   EDITIOy 


Nehi  fork 
THE  MACMILLAN  COMPANY 

LONDON:   MACMILLAN  &  CO.,  Ltd. 

1917 
yiil  rights  reserved 


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Copyright,  1905 
By    the   MACMILLAN   COMPANY 


Set  up  and  electrotyped  April,  1905 

Reprinted  August,  1905,  June,  1906,  February,  1908,  June,  1910, 

January,  1911,  June,  1912,  December,  1917 


Mount  piraaant  ^rraa 

J.  Horace  McFarland  Company 
Harrisburg,  Pa, 


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PREFACE  BY  L.  H.  BAILEY 

My  plan  for  a  series  of  popular  botanical  texts 
contemplated  three  books, —"Lessons  with  Plants," 
primarily  for  the  teacher;  "Botany,"  for  the  school; 
and  "Experiments  with  Plants,"  to  suggest  and  ex- 
plain simple  ways  by  which  the  pupil  could  be  set  at 
the  working  out  of  real  problems  in  the  growth  and 
behavior  of  plants.  The  first  two  books  have  appeared. 
When  I  was  working  on  the  third,  I  chanced  to  visit 
the  laboratory  of  Mr.  Osterhout  at  the  University  of 
California,  at  a  time  when  he  was  instructing  a  class  of 
teachers.  I  saw  at  once  that  he  was  better  fitted  than 
I  to  write  the  book;  and,  finding  that  he  was  contem- 
plating a  similar  text,  I  gave  up  my  enterprise  and 
offered  him  the  title  of  the  proposed  volume.  It  was 
at  first  intended  that  I  collaborate  in  the  preparation 
of  the  book,  but  insistent  duties  have  interposed,  and  I 
have  given  it  no  personal  attention;  moreover,  I  did 
not  feel  that  I  could  add  to  its  usefulness;  and  again, 
a  book  made  by  two  persons  working  so  far  apart,  and 
one  of  them  not  now  actively  engaged  in  teaching, 
would  be  likely  to  lack  homogeneity. 

The  introduction  of  laboratory  work  has  been  the 
great  contribution  of  natural  science  to  pedagogy.  The 
laboratory  sets  the  pupil  at  work  with  a  personal  and 
concrete  problem;  it  develops  the  creative  and  active 


Vi  PREFACE    BY    L.    H.    BAILEY 

faculties,  rather  than  the  receptive;  it  asks  the  pupil 
what  he  has  found  out,  rather  than  what  he  remembers. 
The  school  is  now  reaching  out  to  the  larger  problems 
of  the  environment,  and  to  the  affairs  of  men;  for  it  is  to 
touch  life  at  every  point.  In  this  movement  the  labora- 
tory is  concerned ;  consequently,  the  laboratory  is  de- 
veloping away  from  mere  object -teaching  and  mere 
piece-work,  into  a  vital  and  genuine  touch  with  phe- 
nomena as  they  occur  under  wholly  natural  or  normal 
conditions;  and  there  is  also  a  tendency  toward  the 
development  of  simple  apparatus,  in  order  that  the 
pupil  in  even  the  humblest  school  may  be  reached.  We 
now  see  that  object-lesson  teaching  with  natural  history 
objects,  and  the  giving  of  information  about  nature,  are 
not  nature -study:  we  must  study  the  objects  and  phe- 
nomena in  their  natural  relations.  The  schools  are  now 
ready  for  this  point  of  view.  They  are  growing  plants 
in  windows  when  they  have  no  laboratories  adapted  to 
the  purpose;  some  of  them  are  establishing  school-gar- 
dens; they  are  appropriating  the  adjacent  fields;  and 
they  are  even  drawing  on  private  gardens  and  farms. 
The  ideal  plant  teaching,  it  seems  to  me,  begins  always 
with  function  and  essential  life  relations,  even  with 
young  children.  I  like  the  titles  of  Professor  Oster- 
hout's  chapters, — the  "work"  of  roots  and  leaves  and 
flowers;  and  I  am  glad  that  he  relates  the  subject  to 
the  affairs  of  men  by  including  a  discussion  of  plant- 
breeding. 

College  of  Agriculture  L.   H.   BAILEY. 

Cornell  University,  Ithaca,  N.  Y. 


INTRODUCTION 

The  numerous  questions  which  young  people  ask 
about  plants  are  best  answered  by  themselves.  No 
other  method  gives  vital  knowledge  so  quickly  and 
satisfactorily;  in  no  other  way  is  a  real  grasp  of  the 
subject  obtained.  To  put  them  in  the  way  of  doing 
this  so  far  as  possible  is  the  object  of  this  book.  To 
this  end  familiar  plants  have  been  chosen,  familiar 
utensils  used  in  the  construction  of  apparatus  and 
the  conditions  simplified  as  far  as  may  be.  The  book 
may  be  used  by  both  teacher  and  pupil :  the  order 
of  topics  may  be  followed  or  not,  as  seems  best  under 
the  circumstances. 

In  order  that  the  knowledge  gained  in  the  classroom 
and  out  of  it  may  be  organized,  notes  should  be  kept: 
but  the  note -taking  should  not  be  made  a  burden. 
The  following  outline  of  work  has  been  found  suc- 
cessful. 

1.  The  Question:  this,  it  may  be  said,  should  be 
a  real  one  in  which  the  class  as  a  whole  takes  an  inter- 
est, not  a  formal  affair  in  the  nature  of  an  imposed 
task, 

(vu) 


Vlil  INTRODUCTION 

2.  The  Method:  i.  e.,  how  the  question  is  to  be 
answered,  by  observation  or  by  experiment.  In  the 
latter  case  a  simple  sketch  of  the  apparatus  should  be 
made. 

3.  The  Material:  i.  e.,  what  plants  are  to  be  used, 
how  many  and  in  what  condition. 

4.  Times  of  observation  of  the  experiment,  e.  g., 
every  hour,  every  day,  etc. 

5.  Precautions  AND  sources  of  error:  these  should 
be  discussed  as  fully  as  possible  before  starting  the 
experiment.  Such  discussion  provokes  thought,  criti- 
cism and  lively  interest.  Never  foi^get  to  have  control 
experiments. 

6.  Results:  these  should  be  presented  concisely 
and  clearly,  in  tabular  form  when  possible. 

7.  Conclusions:  distinguish  between  what  is  proven 
and  what  is  indicated  or  rendered  probable.  Dis- 
cordant results  should  be  given  full  consideration :  they 
often  suggest  a  new  experiment  or  a  repetition  under 
modified  conditions. 

8.  Practical  Applications  and  Belated  MaTTERs: 
under  this  head  the  general  .knowledge  and  the  mis- 
cellaneous observations  of  the  class  may  be  organized 
in  a  definite  and  useful  way.  Information  should  be 
obtained  from  farmers,  gardeners  and  other  practical 
men,  the  discussion  of  which  will  often  provoke  new 
questions  and  experiments. 

Notes  may  be  made  under  each  of' these  heads. 


INTRODUCTION  IX 

It  is  advisable  to  use  a  separate  loose  sheet  for  each 
question  or  experiment.  The  drawings  should  be  inked 
with  India  ink;  this  can  be  done  outside  the  class 
room:  a  drawing  ^^w  is  not  necessary  —  any  good  fino 
pen  will  do.  A  single  bottle  of  India  ink  will  supply 
a  class,  as  very  little  is  used. 

Where  each  experiment  is  to  be  done  by  each  indi- 
vidual, a  laboratory  is  necessary:  where  each  is  to  be 
done  by  a  group  or  section  of  the  class,  only  a  limited 
space  is  needed :  where  each  is  done  by  the  class  as  a 
whole,  a  single  shelf  in  front  of  a  window  and  a 
drawer  beneath  to  hold  the  utensils  will  suffice.  For 
most  of  the  experiments  such  plants  have  been  sug- 
gested as  will  grow  even  with  poor  light  and  under 
discouraging  conditions.  This  is  an  especially  impor- 
tant consideration,  in  view  of  the  fact  that  the  average 
schoolroom  is  a  very  poor  place  to  grow  plants. 

While  the  microscopic  work  suggested  is  of  the 
simplest  kind,  it  may  often  be  necessary  to  restrict  it 
to  demonstrations  only  or  to  omit  it  altogether. 

The  principle  involved  is  the  thing  of  prime  impor- 
tance in  all  the  experiments.  Exact  quantitative 
results  are  not  necessary,  nor  is  it  desirable  at  this 
stage  to  spend  much  time  or  effort  in  trying  to  obtain 
them. 

It  may  be  added  that  practically  all  the  experiments 
have  been  successfully  tried  in  the  schools,  many  of 
them  in  the  lower  grades. 


X  I-^  TliOD  rc  TION 

It  gives  me  much  pleasure  to  make  acknowledge- 
ment for  helpful  criticisms  to  Prof.  W.  A.  Setchell, 
Prof.  L.  H.  Bailey,  Prof.  R.  A.  Harper,  and  Prof. 
E.  W.  Hilgard.  For  Figs.  88a  and  151  I  am  indebted 
to  Prof.  R.  H.  Loughridge;  for  Figs.  35  and  36  to 
Prof.  L.  H.  Bailey;  for  Fig.  148a  to  Mr.  C.  K.  Tuttle; 
for  Fig.  103  to  Mr.  N.  L.  Gardner;  for  Figs.  23a,  201 
and  202  to  Mr.  L.  E.  Hunt;  for  Figs.  92,  93,  and  94 
to  Prof.  E.  W.  Hilgard;  for  Figs.  231  to  236  and  240 
to  245  to  Mr.  Luther  Burbank,  and  for  Figs.  249,  250, 
252  and  253  to  Prof.  Hugo  de  Vries.  A  few  figures 
have  been  redrawn  from  English  or  European  sources. 
The  line  drawings  are,  with  few  exceptions,  the  work 
of  Mr.  H.  N.  Bagley,  and  the  photographs,  except 
as  noted  above,  are  by  Mr.  B.  F.  White. 

Berkeley,  Cal.  W.  J.  V.  OSTERHOUT. 

January,  1905. 


CONTENTS 


CHAPTER  PAGE 

Introduction v 

I.     The  Awakening  of  the  Seed 1 

II.     Getting  Established 89 

III.  The  Work  up  Roots 87 

IV.  The  Work  of  Leaves 163 

V.     The  Work  of  Stems 224 

VI.     The  Work  op  Flowers 286 

VII.     The  Work  of  Fruits 312 

VIII.     How  Plants  are  Influenced  by  Their  Surroundings  .    .  326 

IX.     Plants  Which  Cause  Decay,  Fermentation  and  Disease  .  361 

X.    Making  New  Kinds  of  Plants 406 

Index 455 


(xi) 


LIST    OF    ILLUSTRATIONS 

FIG.  PAGB 

1  Horse-bean 1 

2  Horse-bean  opened 1 

3  Castor-bean 2 

4  Castor-bean  opened 2 

5  Corn 3 

6  Corn  cut  lengthwise 3 

7  Sunflower  seed 3 

8  Sunflower  seed  opened 3 

9  Peanut 4 

10  Peanut  opened 4 

11  Arrangement  for  keeping:  seeds  on  ice 5 

12  A  bottle  containing  seeds,  filled  with  water  and  corked  air-tight 5 

13  A  method  of  determining  whether  air-dry  seeds  contain  water 7 

14  A  bean  placed  in  water,  showing  successive  stages  in  the  process  of 

wrinkling 8 

15  A  method  of  determining  whether  openings  exist  in  the  seed-covers ....  8 

16  An  arrangement  for  holding  seeds  while  under  water 9 

17  A  home-made  balance  constructed  of  umbrella  wire 13 

18  A  modification  of  the  balance 14 

19  A  method  of  keeping  seeds  half-submerged,  in  order  to  discover  how 

the  water  enters 15 

20  Seed-covers  floating  on  water 16 

21  Modification  of  the  experiment  shown  in  Fig.  20 19 

22  Scarlet  Runner  Bean  opened,  showing  the  pocket  into  which  the  caulicle 

fits 20 

23  Seeds  half-submerged  in  wet  sand,  to  determine  how  the  water  enters. .  21 
23a  Three  rows  of  corn  planted  at  the  same  time,  each  grain  being  half- 
buried  in  the  moist  soil 22 

24  "Walnut  divided  in  half,  showing  the  wick-like  central  strand 23 

25  Seeds  placed  in  a  saturated  atmosphere 26 

26  Another  method  of  keeping  seeds  in  a  saturated  atmosphere 27 

27  Method  of  maintaining  a  saturated  atmosphere  and  a  constant  water- 

level  27 

28  Method  of  testing  the  permeability  of  the  seed-cover  to  air 30 

(xiii) 


XIV  LIST    OF    TLFATSTEATIONS 

FIG.  PAGE 

29  Seeds  on  wet  sand  with  different  amounts  of  aii'  at  their  disposal 33 

30  Apparatus  for  determining  whether  germinating  seeds  produce  carbon 

dioxide 34 

31  Method  of  measuring  the  amount  of  carbon  dioxide  produced  by  ger- 

minating seeds 34 

32  Method  of  measuring  the  temperature  of  germinating  seeds 36 

33  Method  of  determining  whetlier  air  exists  in  the  soil 37 

34  Apparatus  for  determining  how  deep  seeds  should  be  planted 39 

35  A  planting  stick 40 

30     Screens  for  seed-beds 41 

37  Method  for  testing  the  permeability  of  the  seed -cover  to  heat 42 

38  Arrangement  for  testing  the  swelling  power  of  a  single  seed   49 

39  Arrangement  for  testing  the  swelling  power  of  a  mass  of  seeds 51 

40  Apparatus  for  demonstrating  that  swelling  seeds  exert  pressure 53 

41  Bottle  broken  by  swelling  seeds 54 

42  Germination  of  Squash 54 

43  Later  stage  of  germination  of  Squash 54 

44  Squash  seeds  arranged  for  germination  experiment 55 

45  Germinating  Cocoanut  cut  lengthwise 57 

46  Buckeye  cut  open 58 

47  Buckeye.     Plumule  emerging  from  between  elongated  stalks  of  seed- 

leaves  ' 59 

48  Buckeye.     A  later  stage 59 

49  Buckeye.     A  still  later  stage 60 

50  Scarlet  Runner  Bean  germinating 00 

51  Apparatus  for  demonstrating  that  osmosis  exerts  pressure 61 

52  Apparatus  for  measuring  pressure  due  to  osmosis 62 

53  Section  of  a  bit  of  the  seed-leaf  of  the  Horse-bean 65 

54  Water-bath  67 

55  Filaree  seeds  burrowing  into  cotton 70 

56  Corn  making  its  way  above  ground 71 

57  Bean  getting  above  ground 71 

58  Castor-bean  twisting  itself  into  a  loop 72 

59  Apparatus  for  measuring  the  force  of  the  upwai'd  growth  of  the  plant. .  73 

60  Modification  of  apparatus  shown  in  Fig.  59 74 

61  Arrangement  for  weighting  an  upward-growing  stem 75 

62  Modification  of  arrangement  shown  in  Fig.  61 75 

63  Bean  with  stem  marked  to  determine  region  of  greatest  growth 77 

64  Contrivance  for  marking  stems  in  manner  shown  in  Fig.  63 78 

65  Scarlet  Runner  Bean  with  top  (terminal  bud )  removed 79 

(i6     Radish  seedlings  growing  upward  along  the  glass  side  of  a  box 79 

67  Sunflower  seedlings  penetrating  the  soil 80 

68  Squash  seedlings  endeavoring  to  penetrate  the  soil 81 


LIST   OF    ILLUSTRATIONS  XV 

wo.  PAGE 

69  Apparatus  for  deterniiiiing  how  much  force  the  root  exerts  in  growing 

downward 82 

70  Apparatus  for  determining  force  of  growth  of  a  root 84 

71  Root  marked  in  order  to  determine  the  region  of  greatest  growth 85 

72  Plant  attached  to  support  ready  to  have  root  cut  off 87 

73  Seeds  pinned  to  corks  which  are  floating  on  water 88 

74  Seeds  arranged  with  caulicles  resting  on  mercury 89 

75  Arrangement  for  causing  germinating  seeds  to  revolve  slowly 91 

76  Water-wheel  for  making  germinating  seeds  revolve  rapidly 93 

77  Arrangement  for  testing  effect  of  moisture  on  direction  of  growth  of 

roots 95 

78  Arrangement  to  test  behavior  of  roots  in  moist  air 90 

79  Arrangement  for  ascertaining  whether  roots  grow  in  the  direction  of 

moisture 96 

80  Apparatus  for  observing  behavior  of  roots  as  they  encounter  obstacles.     97 

81  Apparatus  designed  to  test  behavior  of  side  roots  under  the  influence 

of  gravity 98 

82  Modification  of  apparatus  shown  in  Fig.  80 99 

83  Radish  seedlings  showing  root-hairs 100 

84  Root-hairs  of  Radish 101 

85  Cutting  of  Wandering  Jew  in  water,  showing  root-hairs 102 

86  Apparatus  for  measuring  rate  of  evaporation  from  a  saturated  soil 114 

87  Method  of  supplying  water  to  apparatus  shown  in  Fig.  86 114 

88  Four  lamp-chimneys  filled  with  soil  for  the  purpose  of  studying  tlie 

evaporation 115 

88rt  New  growth  on  cultivated  and  uncultivated  Apricot  trees 11(1 

89  Diagram  of  fairly  dry  soil  showing  relations  of  root-hair  to  surround- 

ing particles lli> 

90  Cross-section  of  a  root  as  it  grows  in  the  soil 120 

91  Artificial  root-hair 123 

92  Diagram  to  illustrate  effect  of  ideal  plowing ]2(i 

93  Part  of  furrow  slice  (of  Fig.  92)    magnified  to   show  floccules  or   soil- 

crumbs  ; 127 

94  A  single  soil-crumb  magnified 128 

95  A  still  for  making  distilled  water  ];!7 

96  The  result  of  a  water  culture  of  Wandering  Jew 140 

97  Apparatus  to  determine  whether  the  root  excretes  acid  143 

98  Tubercles  on  roots  of  Clover 149 

99  Two  Scarlet  Runner  Beans  of  the  same  age,  from  one  of  which  the 

seed-leaves  were  removed  shortly  after  germination 163 

100  Germinating  Date 180 

101  Leaf  of  English  Ivy  deprived  of  starch  and  placed  in  water 182 

102  Arrangement  for  excluding  light  from  a  part  of  the  leaf 182 


XVI  LIST    OF    ILLUSTRATIONS 

FIG.  PAGE 

103  Two  lots  of  Squash  seedlings  of  the  same  age,  one  grown  in  light,  the 

other  in  darkness 184 

104  A  seedling  of  Castor-bean 186 

105  Apparatus  for  the  decomposition  of  starch 186 

106  Air-pump 187 

107  Details  of  piston  of  air-pump 188 

108  Air-pump  witb  automatic  arrangement  to  prevent  piston  from  slipping 

back 190 

109  Details  of  piston  of  air-pump 190, 

110  Arrangement  for  investigating  the' power  of  a  leaf  to  "restore"  air 

which  has  been  "  vitiated  "  by  a  burning  candle 191 

111  Arrangement  for  collecting  gas  given  off  bj'  a  water-plant  in  sunlight     192 

112  Apparatus  for  growing  a  leaf  in  air  deprived  of  carbon  dioxide 193 

113  Section  of  leaf  of  common  wild  Yellow  Mustard 198 

114  Section  of  leaf  of  Iris 199 

115  A  single  chlorophyll  grain 201 

116  A  single  cell  of  a  leaf  with  chlorophyll  grains 202 

117  Arrangement  for  determining  whether  leaves  give  off  water  vapor....  203 

118  Method  of  inserting  a  leaf-stalk  air-tight  in  a  rubber  stopper 205 

119  Apparatus  for  measuring  transpiration  of  a  leaf 206 

120  Diagram  showing  in  section  and  surface  view  the  form  and  position 

of  guard-cells  when  closed  and  open 208 

121  Guard-cells  and  neighboring  cells  of  epidermis 209 

122  Artificial  stoma  and  guard-cells 210 

123  Modification  of  part  of  apparatus  shown  in  Fig.  122 211 

124  Acacia  leaf,  night  or  sleep  position 218 

125  Acacia  leaf,  day  position 218 

126  Leaf  mosaic  of  Ivy  Geranium 219 

127  Leaf  mosaic  of  Chestnut 219 

128  Upright  branch  of  Periwinkle 220 

129  Same  branch  seen  from  above 220 

130  Horizontal  (trailing)  branch  from  same  plant 221 

131  Diagram  of  cross-section  of  Squash  stem 224 

132  Corn-stalk 225 

133  Stem  of  Squash  (microscopic  structure) 227 

134  Cross-section  of  a  bundle  of  Corn 231 

135  Oak  branch  ( microscopic  structure ) 232 

136  Bordered  pit,  cut  in  half 234 

137  Simple  pit,  cut  in  half 234 

138  Pine  branch  (microscopic  structure)  236 

139  Method  of  injecting  a  twig  by  means  of  the  air-pump 237 

140  Arrangement  for  forcing  water  through  a  branch 238 

141  Modification  of  arrangement  shown  in  Fig.  140 240 


LIST   OF   ILLUSTRATIONS  ^yil 

FIG,  PAGE 

142  Method  of  measuring  the  amount  of  bleeding  from  a  stump  (root  pres- 

sure)    243 

142a  Buttress  formed  on  the  lower  side  of  a  branch 248 

143  Terminal  part  of  a  growing  branch  showing  the  three  regions  of  growth    249 

144  Bud  of  Brussels  Sprouts  cut  lengthwise 250 

145  Portion  of  tree  trunk  near  a  burl 262 

146  Diagram  showing  eftect  of  weight  applied  to  end  of  a  beam 265 

147  Diagram  of  a  girder 266 

148  Diagram  showing  the  g'rder-like  arrangement  of  strengthening  tissues 

in  a  Bulrush 267 

149  Cross-section  of  a  portion  of  a  Cabbage  leaf 237 

150  Collenchyma 268 

151  Clematis  climbing  on  an  evergreen 271 

152  Behavior  of  a  strip  of  flower-stalk  of  Dandelion  in  water 273 

153  Branch  of  English  Ivy 275 

154  Method  of  investigating  lenticels 279 

155  Method  of  investigating  entrance  of  air  into  stem  by  way  of  stomata  280 

156  Method  of  investigating  entrance  of  air  into  stem  by  way  of  stomata 

and  lenticels 281 

157  Willow  twig  suspended  in  a  saturated  atmosphere 281 

158  Apparatus  for  supplying  air  in  a  constant  stream  to  an  aquarium 283 

159  Arrangement  for  supplying  carbon  dioxide  to  plants  growing  in  water   284 

160  Arrangement  for  growing  water-plants  in  contact  with  a  bubble  of 

carbon  dioxide  or  air ...  285 

161  Cherry  blossom  cut  open  to  show  the  parts  of  the  flower 288 

162  Ovary  (seed-case)  of  Oat,  with  feathery  style     290 

163  Branch  of  the  style  of  Oat,  with  germinating  pollen-grain 290 

164  Embryo  sac  of  a  Lily  291 

165  Hanging  drop  arrangement  for  the  cultivation  of  pollen-grains 293 

166  Flowers  of  Gaillardia  cut  open 303 

167  Flower  of  Iris,  showing  how  the  stigma  removes  pollen  from  the  bee,  etc.  304 

168  Flowers  of  Partridge  berry  cut  open 305 

169  Flowers  of  Sage  cut  open 306 

170  Fruit  of  Squirting  Cucumber  in  the  act  of  expelling  the  seeds 321 

171  Clematis  fruit,  which  flies  by  means  of  the  feathery  style 322 

172  Linden  fruit,  which  flies  by  means  of  a  wing-like  bract 322 

173  Hop  fruit,  which  flies  by  means  of  a  bract 323 

1 74  Maple  keys,  which  fly  by  means  of  a  wing 323 

175  Burdock  head 323 

176  Fruit  of  Bur  Clover 324 

177  Fruit  of  Beggar's-ticks 324 

178  Fruit  of  Clotbur 324 

179  Potato  which  had  been  allowed  to  sprout  and  grow  on  a  dry  table 327 


Xviii  LIST    OF    ILLUSTRATIONS 

FIG.  PAGE 

180  Potato  showing  the  effect  of  light  and  dryness  on  growth 328 

181  Sprout  of  Prickly  Pear  grown  in  the  dark 329 

182  A  spherical  Cactus 331 

183  Branch  of  Cytisus 332 

184  Stems  of  Callitriche  in  cross-section 333 

185  Epidermis  of  Holly 334 

186  Waxy  covering  of  Sugar  Cane 334 

187  Hairs  of  Wormwood  or  Sage  Brush 334 

188  Hairs  of  Mullein 335 

189  Cross-section  of  stem  of  Water-polygonum  grown  in  dry  soil 335 

190  Cross-section  of  stem  of  Water-polygonum  grown  in  water 335 

191  Upper  epidermis  of  Water-polygonum 336 

1 92  Cross-section  of  a  leaf  of  Oleander 337 

193  Arrowhead,  showing  effect  of  submersion  on  leaves 337 

194  Cross-section  of  the  ribbon-shaped  leaves  of  Arrowhead 338 

195  Leaves  of  Water-buttercup  (water-leaf  and  air-leaf) 339 

196  Lower  epidermis  of  Water-polygonum 340 

197  Leaves  of  Dandelion,  normal  and  in  saturated  atmosphere 342 

198  Gorse,  normal  and  in  saturated  atmosphere 343 

199  Leaves  of  Prickly  Lettuce  (sun-  and  shade-leaves) 344 

200  Beech  leaves  (sun-  and  shade-leaves) 345 

201  The  effect  of  wind  on  the  growth  of  a  tree  trunk' 348 

202  Shows  how  branches  are  stunted  and  killed  on  the  windward  side 349 

203  The  result  of  having  branches  mainly  on  one  side  (as  in  preceding 

figure ) 350 

204  Branch  of  Ivy  Geranium 354 

205  Different  kinds  of  bacteria 362 

206  Steam  sterilizer 363 

207  Tumbler  containing  a  slice  of  boiled  potato 365 

208  A  scraping  from  a  potato  culture 367 

209  Funnel  with  neck  removed  so  as  to  fit  into  a  tumbler 369 

210  Flat  bottle  containing  gelatin  (for  "plate  culture  ") 370 

211  Chart  showing  the  distribution  of  cholera  cases  in  the  Hamburg  epi- 

demic of  1892 373 

212  Stab  cultures  in  gelatin 375 

213  Yeast-cells  budding 390 

214  Black  Mould  of  bread 391 

215  Same  beginning  to  show  spores  at  the  edges  of  the  bread 392 

216  More  advanced  stage  of  spore  formation 393 

217  Portion  of  the  mycelium 394 

218  Black  Mould  of  bread  showing  manner  in  which  mycelium  sends  out 

root-like  branches  at  short  intervals 395 

219  A  single  spore  case  of  the  Black  Mould  of  bread 395 


LIST    OF    ILLCSTIiATIOyS  XIX 

220  Formation  of  zygosi»ores  of  tlie  Black  Mould  of  bread .'{90 

221  Green  Mould  of  cheese 397 

222  Spore  of  Corn-Smut  germinating 398 

223  Spore  of  Corn-Smut  producing  conidia 399 

224  Summer  Spores,  or  uredospores  of  the  Black  Stem  Rust  of  Wheat 402 

225  Autumn  spores,  or  teleutospores  of  the  Black  Stem  Rust  of  Wheat 402 

22G  Summer  spores  of  the  Black  Stem  Rust  of  Wheat,  germinating  on  a 

Wheat  leaf  and  sending  the  germ  tubes  through  the  stomata 402 

227  Autumn  spores  of  the  Black  Stem  Rust  of  Wheat  producing  conidia  . .  403 

228  Section  of  Barberrj-  leaf  showing  Rust 403 

229  Cluster-cup  of  Black  Stem  Rust  of  Wheat 404 

230  Perithecium  of  the  common  Mildew  of  the  Lilac 407 

231  Increased  size  due  to  hybridization  (without  selection)  411 

232  Increased  size  due  to  selection  (without  crossing) 411 

233  Improved  Beach  Plum 413 

234  Branch  of  Improved  Beach  Plum 414 

235  The  Plumcot,  a  cross  between  the  Plum  and  the  Apricot  415 

236  The  Stoneless  Plum  and  its  parents 416 

237  Curve  of  variation 418 

238  Assymmetrical  curve  of  variation 419 

239  Double  curve  of  variation 419 

240  Shasta  Daisy  and  its  American  parent 423 

241  Shasta  Daisy,  variations 424 

242  Shasta  Daisy,  double 425 

243  Variation  in  leaves  of  hybrid  Blackberries 426 

244  Variation  in  stems  of  hybrid  Blackberries 427 

245  Variation  in  leaves  of  hybrid  Poppies 429 

246  Plum  blossom,  with  anthers  and  petals  removed 431 

247  Flowers  of  Lamarck's  Evening  Primrose 444 

248  Lamarck's  and  Dwarf  Evening  Primrose 445 

249  Leaves  of  Lamarck's  and  Broad  Evening  Primrose 446 

250  Seedlings  of  Lamarck's,  Pale  and  Broad  Evening  Primrose 447 

251  Four-,  five-  and  seven-leaved  Clover 448 

252  Ten-leaved  Clover 449 

253  Atavistic  Clover 449 


EXPERIMENTS  WITH    PLANTS 


CHAPTER  I 


THE  AWAKENING  OF  THE  SEED 


What  is  a  seed  ?    Study  as  types  of  seeds  the  Horse- 
bean  (or  Other  large  bean),  the  Castor-bean  and  Corn. 

The  Hokse-bean. — Examine  some  dry  and  some 
soaked  Horse-beans.  Notice  the 
shape  and  appearance  (color,  mark- 
ings, surface,  etc.)  of  the  seed. 
The  large  black  scar  (hilum)  at  the 
end  of  the  seed  (Fig.  1)  is  the 
place  of  attachment  to  the  pod. 

Remove   the    cover,    notice    its 
texture,     thickness,    etc. ;     is    the 
c   __    pi 


Horse-bean;    the  scai 
(hilum)  at  (A). 


2.  Horse-bean  opened,  show- 
ing the  two  seedleaves(sO. 
the  caiilicle  (c)  and  the  plu- 
mule (jtl). 


cover  everywhere 
closely  applied  to  the  germ?  Within 
the  cover  are  two  thickened  halves, 
the  seed-leaves  (Fig.  2,5/)  attached 
to  a  short  rod-like  body,  the  cau- 
licle  (c) ,  at  one  end  of  which  is  a 
cluster  of  very  small  leaves,  called 
the  plumule  (^Z),  which  may  be 
easily  studied  with  a  hand- lens,  or 
(1) 


EXPERIMEXTS    WITH    PLANTS 


even  with  the  naked  eye  :  these  develop  into  foliage 
leaves.  The  seed-leaves,  caulicle  and  plumule  together, 
make  up  the  germ  or  embryo  plant.  The  seed  of  the 
Horse-bean,  therefore,  consists  of  an  embryo  plant 
provided  with  a  cover. 

The  Castor-bean.^ — The  seed  somewhat  resembles 
a  beetle  in  shape  and  color.    Its  scar  (hilum)  is  covered 


Vi 


ea 


3.  Castor-bean;  at  {ca)  the  car- 
uncle, a  spongy  body  which 
absorbs  water  diiring  ger- 
mination; the  scar  (hihim) 
is  concealed  by  it. 


4.  Castor- bean  opened,  showing 
endosperm  (e),  caulicle  (c). 
seed-leaves  (si)  and  caruncle 
(ca). 


by  a  spongy  body  (the  caruncle.  Fig.  3,  ca) .  '  The  cover 
has  a  very  different  texture  from  that  of  the  Horse- 
bean  cover  and  fits  loosely.  The  seed-leaves  (Fig.  4) 
are  thin  and  delicate  in  appearance,  with  prominent 
veins  ;  the  caulicle  and  plumule  are  much  smaller  than 
in  the  Horse-bean.  Outside  the  seed-leaves  is  a 
white  oily  substance  which  surrounds  the  germ  but  is 
not  attached  to  it:  it  is  called  endosperm  (Fig.  4,  e) . 
The  Corn.— Both  dry  and  soaked  grains  should  be 
used.  In  the  Corn  (Fig.  5)  the  seed-case  adheres  to 
the  seed  and  forms  the  outer  layer  of  the  seed --cover, 

^  This  i.s  poisonous  and  should  not  be  eaten. 


THE   AWAKENING    OF    THE   SEED 


5.     Corn,  the  germ  is 
located  at  [g) . 


6.  Corn  cut  lengthwise, 
showing  caulicle  (c) ,  plu- 
mule {pD,  seed  leaf  (0 
and  endosperm  (e). 


which  is  thin,  transparent  and  fits  snugly.  If  we 
cut  through  the  grain,  as  shown  in  Fig.  6,  we  see 
the  germ,  consisting 
of  a  single  seed- 
leaf  {I)  with  cau- 
licle, plumule  and  a  «/. 
large  mass  of  en- 
dosperm, which  in 
Sugar  Corn  is  clear  ^ 
and  sugary,  while 
in  ordinary  Corn 
it  is  hard  and  yellow  on  the 
outside,    but    floury    toward    the    center. 

in  some  plants  the  seed  is  covered  only  by  the  seed- 
coat  (the  skin  of  the  bean  is  such 
a  seed -coat),  while  in  others  it  is 
covered  by  the    seed-coat    plus   a 
part  of    the   seed-case    (the   seed- 
case  corresponds  to  the  pod  of  the 
bean) ;  the  seed- case  may  be  con- 
solidated  with    the    seed-coat, 
as  in  the  Corn,  or  be  separate 
from   it,   as    in   the    Sunflower 
(Figs.  7  and  8),  Peanut  (Figs. 
9   and  10),  Walnut   (Fig.  24), 
Peach,   etc.     When   the    seed- 
case,   or  any  part  of  it,  remains        8.   SunHower  seed  opened,  showing 

attached  to  the  seed  the  whole         "r^-ieLt^lso"""''  ^'^  "^ 


Sunflower  seed. 


EXPERIMENTS    WITH   PLANTS 


is  called  a  fruit,  but  for  convenience  we  may  speak 
of  it  as  a  seed;  its  covering  we  may  call  a  seed-cover, 
whether  it  be  a  simple  seed- coat  or  some- 
thing more. 

Obtain  all  the  seeds  you  can  which  are 
large  enough  for  study  (including  those  of 
common  fruits,  flowers,  cereals,  etc.),  com- 
pare them  carefully  with  the  types  we  have 
just  studied:  discover  the  germ  in  each  one 
9.  Peauut.  and  study  it  with  especial  care. 
As  the  result  of  this  comparison,  we  may  con- 
clude that  a  seed  is  an  embryo  plant  provided  with 
a  cover,  and  in  some  cases  with 
endosperm:  before  germination 
it  is  in  a  sleeping  or  dormant 
condition. 

What  is  needed  to  awaken 
the  seed  ?  Many  persons  will 
say  that  water  and  warmth  are 
necessary.  Place  some  seeds 
in  moist  sawdust  in  a  place 
warm  enough  to  ensure  germi- 
nation. The  sawdust  should  be  merely  moist  (not  so 
wet  that  water  can  be  squeezed  out  of  it  by  the  hand) , 
and  may  be  placed  in  boxes,  pots  or  cans,  which  must 
have  holes  provided  in  the  bottom  for  drainage:  plant 
the  seeds  about  an  inch  deep. 

Place  some  seeds  of  the  same  kind  on  ice,  as  shown 


10.  Peanut  opened  showing  can- 
licle  (c).  plumule  ipl)  and  seed- 
leaf  {sLh 


THE   A  WAKENING    OF    THE   SEED 


in  Fig.  11.  Obtain  a  box  measuring  about  eighteen 
inches  each  way,  place  it  in  a  larger  box,  and  fill  the 
space  between  the  boxes  with  dry  sawdust;  place  the 
ice  in  the  inner  box  and  surround  it  with  dry  saw- 
dust; enclose  the  soaked  seeds  in  a  piece  of  mosquito 
netting  (to  prevent  losing  them)  and  place  them  on 
the  ice;  cover  them  with  moist  sawdust  (the  melting 
ice  will  keep  it  continually  moist) .  Fifteen  pounds  of 
ice  will  last  several  days  under  these  conditions. 

Place  other  seeds  of  the  same  sort  under  water:  it 
suffices  to  simply  put  the  seeds  in  a  bottle,  which  is 
then  submerged  in  water  and  tightly  corked  while 
under  water,  taking  care  to  exclude  all  air-bubbles. 
Vaseline  may  be  smeared  over  the  cork 
to  make  it  air-tight  (Fig.  12).  Air  may 
be  expelled  from  the  water  by  boiling  it 
for  several  minutes  just  before  using,  but 


11.  Arrangement  for  keeping  seeds  on  ice:  the  spare 
between  the  boxes  is  tilled  with  sawdust,  which 
also  surrounds  the  ice. 


12.  A  bottle  con- 
taining seeds, 
filled  with  water 
and  corked  air- 
tight, to  test  the 
power  of  seeds  to 
germinate  with- 
out air. 


6  uxpiJRiMEyrs  with  plants 

this  is  ill  most  cases  unnecessary.  It  is  advisable  to 
wire  the  cork  firmly  in  place,  since  a  certain  amount 
of  gas  is  given  off  by  the  seeds,  which  may  force  it 
out  of  the  bottle. 

For  this,  as  well  as  for  subsequent  experiments  on 
seeds,  it  is  well  to  select  kinds  which  germinate  quickly, 
such  as  Horse-bean,  Lima  Bean  (or  other  kinds  of 
beans).  Sunflower,  Pea,  Lupine,  Radish,  Squash, 
Wheat  and  Corn. 

It  will  appear  from  this  experiment  that  the  seed 
needs  a  sufficient  amount  of  water,  air  and  warmth, 
in  order  to  grow.  Every  need  of  the  plant  presents 
a  prohlem  for  the  plant  to  solve.  Some  plants  supply 
their  needs  in  what  seems  to  be  the  best  possible  way, 
while  others  adopt  methods  which  appear  much  less 
efficient.  We  may  say  that  the  plant  solves  its  prob- 
lem well  or  ill,  though  in  so  speaking  we  do  not  mean 
to  imply  that  the  plant  thinks  or  consciously  adapts 
means  to  ends,  since  we  are  convinced  that  this  can- 
not be  the  case.  The  problems  which  plants  are  called 
upon  to  solve  are  very  numerous,  and  the  penalty  of 
solving  them  poorly  is  to  die,  or  be  crowded  out  by 
more  successful  competitors.  In  studying  the  plant, 
we  should  try  first  of  all  to  discover  its  needs  and  then 
try  to  think  out  for  ourselves  in  each  case  the  best 
solution  of  the  problem  involved. 

Let  us  consider  first  the  problem  of  tvater.  How 
much  water  does  the  embryo  plant  require,  and  how 


THE    AWAKENING    OF    THE    SEED 


is  it  obtained !  Do  seeds  in  their  ordinary  dry  condi- 
tion contain  water?  We  may  answer  this  question  by 
placing  some  seeds  in  one  end  of  a  glass  tube  (a  test- 
tube  is  most  convenient,  but  any  glass  tube  a  few 
inches  long  will  answer;  a  tin  cup  covered  with  a 
piece  of  glass  answers  every  purpose)  and  heat- 
ing the  end  where  the  seeds  are  placed  (Fij 
13) .  If  moisture  is  present  it  will  be  driven 
off  and  condense  in  drops  toward  the 
cooler  end,  which  should  be  left  open.^ 
Explain    the   popping   of   Pop -corn. 

The  amount  of  moisture  in  the 
seed  greatly  affects  its  preserva- 
tion (see  page  45). 

How  does  the  seed  absorb 
water  ?  Place  in  water  a  lot 
of  seeds  of  the  same  kind, 
as  nearly  alike  as  possible  in 
size,  shape  and  color,  keep- 
ing other  similar  seeds  dry 
for  comparison.  An  interest- 
ing series  for  study  is  the  Pea,  Lima  Bean,  Castor- 
bean,  Filbert  (or  some  other  nut).  Radish,  Flax  or 
Quince.    Observe  constantly  for  half  an  hour,  and  after 

1  If  no  moisture  can  be  detected  by  this  method,  weigh  out  three  or  four 
ounces  of  seeds,  heat  them  for  some  time  in  an  oven  or  wherever  they  will 
not  be  scorched,  and  reweigh.  Any  loss  of  weight  is  due  to  moisture  driven 
off  by  the  heat.  By  heating  on  a  water-bath  (Fig.  54)  untilthey  cease  losing 
weight,  the  exact  percentage  of  moisture  may  be  ascertained  by  dividing  the 
loss  in  weight  by  the  original  weight. 


8 


EXPERIMENTS    mTH    PLANTS 


that  at  frequent  intervals.     Notice  whether  soaking  af- 
fects the  size,  color  or  texture.    Does  the  cover  wrinkle: 


14.    A  Bean  placed  in  water,  showing  successive  stages  in  the  process  of  wrinkling;  the 
wrinkling  indicates  where  the  water  enters  and  how  it  spreads  inside  the  cover. 

if  so,  where  does  the  wrinkling  commence,  and  in  what 
direction  does  it  progress?  (See  Fig.  14.)  Does  this  in- 
dicate where  water  first  enters  the  seed  ?    What  causes 

the  wrinkles  ?  Why  do 
they  disappear  after  a 
time  ?  Do  the  covers 
appear  to  hinder  the 
water  from  being  ab- 
sorbed by  the  germ? 
Consider  the  appar- 
ently water -proof 
covers  of  the  Castor- 
bean,  Buckeye,  etc. 
Would  it  not  be  an 
obvious  advantage  to 
have  openings  in  the 
cover  through  which 
the  water  might  enter 
more  rapidly?  Are 
~^^^  there  such  openings 

15.    A  method  of  determining  whether  openings  exist  in        •      j.<       QPPd-rOvei**;  ^ 
the  seed-covers.  ^■^  LilC  0CCU-I./UVCI0  . 


THE    AWAKENING    OF    THE    SEED  9 

Place  the  seeds  in  water  and  heat  (Fig.  15) ;  stir  the 
water  to  remove  the  bubbles  that  form  on  the  seeds; 
keep  the  seeds  submerged;  if  necessary,  hold  them 
under  water  by  a  piece  of  glass  or  wire  netting  or  by 
placing  them  in  a  wire  spring  (see  Fig.  16) .  Do  you 
find  openings:  how  many  and  where  located  I  Test 
as  many  seeds  as  you  can  in  this  way.  (The  Squash, 
Walnut,  Pecan  and  Brazil-nut  give  striking  results; 
the  Castor-bean  is  apt  to  be  somewhat  puzzling;  the 
Filbert  seems 
to  have  a  good 
many  openings; 
do     they     pass 

t  h  r  O  U  2"  h       the        ^^'    ^^  arrangement  for  holding  seeds  while  under  water. 

shell  into  the  cavity?)  Many  seed -covers  become 
cracked  in  the  course  of  time ;  distinguish  between  such 
cracks,  which  may  occur  anywhere,  and  openings  which 
occur  constantly  in  the  same  place. ^ 

If  any  of  the  seeds  do  not  yield  bubbles  when 
placed  in  warm  water  it  does  not  necessarily  mean  that 
there  is  no  opening;  it  may  simply  denote  a  lack  of 
air  in  the  seed.  Such  seeds  may  be  further  tested  by 
soaking  thoroughly,  wiping  the  surface  dry  and  squeez- 
ing to  see  where  water  is  pressed  out.  Or,  in  the 
ease  of  nuts,    etc.,    any   part   of  the   shell   where   an 

1  Where  the  cover  consists  of  an  outer  and  an  inner  part  (i.  e.,  seed-coat 
proper  plus  the  seed-case),  as  in  the  Walnut.  Pecan  and  Filbert,  the  outer  por- 
tion is  of  principal  interest  but  the  inner  one  may  also  be  tested  after  the  outer 
is  removed.     The  shell  of  the  Brazil-nut  is  a  true  seed-coat. 


10  JSXPERIMENTS    WITH    PLANTS 

opening  is  suspected  to  exist  may  be  sealed  to  the 
end  of  a  tube,  which  should  then  be  placed  under 
water  and  blown  into  forcibly  (see  page  31).  We 
may  also  place  the  seeds  in  an  air-pump  and  exhaust 
(see  page  187). 

Does  most  of  the  water  enter  through  these  open- 
ings ?  One  way  to  find  out  is  to  stop  up  the  opening, 
then  submerge  the  seed  and  note  how  much  the  ab- 
sorption of  water  is  thereby  hindered  (as  compared 
with  untreated  seeds  which  are  submerged  at  the  same 
time).  A  good  substance  for  closing  the  opening  is 
rubber  cement  (the  kinds  used  for  repairing  bicycle 
tires  are  good  and  easily  obtainable) ,  or  melted  rubber 
applied  hot  (prepared  by  melting  good  black  rubber 
in  a  spoon) ;  if  the  latter  is  used,  place  whiting  or 
flour  on  the  surface  of  the  rubber  (after  it  is  applied 
to  the  seed)  to  prevent  it  from  sticking  to  other  ob- 
jects. Try  to  cover  the  opening  only:  it  is  difficult, 
however,  to  avoid  covering  at  the  same  time  the  adja- 
cent portions  of  the  seed.  Thus,  in  the  case  of  the 
Horse-bean,  the  scar  is  apt  to  get  covered.  Since 
this  is  apparently  more  porous  than  the  rest  of  the 
cover,  it  may  be  that  it  admits  water  readily;  hence 
in  covering  it  we  are  perhaps  introducing  an  error. 
This  may  be  offset  if  we  cover  an  equal  area  (includ- 
ing the  scar)  in  the  control  seeds  (i.  e.,  those  which 
do  not  have  the  openings  covered)  without  interfer- 
ing with  the  opening. 


THl^J    AWAKENING    OF    THE    SEED  11 

Weigh  both  sets  of  seeds  (i.  e.,  the  control  and 
the  others;  there  should  be  at  least  twenty  in  each 
set),  treat  them  with  rubber  or  cement,  and  weigh 
again. 

Before  proceeding  with  the  experiment,  test  the 
seeds  to  see  if  the  openings  are  stopped.  Place  some 
untreated  seeds  in  water  (the  control  seeds  must  not 
be  used  for  this) ,  and  heat  until  bubbles  begin  to  issue 
from  the  openings  of  all  of  them;  then  place  the 
treated  seeds  in  the  warm  water;  if  no  bubbles  issue 
from  them  we  may  consider  it  fairly  certain  that  they 
are  satisfactorily^  closed;  the  heat  must  not  be  too 
great  or  too  prolonged,  as  it  may  in  that  case  soften 
the  rubber  so  that  the  expanding  air  inside  may  force 
an  opening.  Should  any  of  the  sealed  seeds  yield 
bubbles,  it  is  better  to  throw  all  the  sealed  seeds  away 
and  prepare  a  fresh  lot,  until  you  succeed  in  getting 
them  all  air-tight. 

Submerge  all  the  seeds  in  cold  water  (the  wire 
spring  shown  in  Fig.  16  is  useful  for  keeping  them 
under  water;  the  seeds  may  be  placed  in  it  and 
weighed,  together  with  the  spring,  thus  making  it  un- 
necessary to  handle  them  separately) .  Remove  the 
seeds  at  frequent  intervals,  dry  them  on  the  surface 
and  weigh  both  sets,  to  see  which  is  absorbing  water 
more  rapidly.  Any  seeds  with  cracks  in  the  covers 
must,  of  course,  be  rejected.  At  the  end  of  the 
experiment,  place  the  seeds  again  in   warm  water,  to 


12 


EXPERIMENTS    WITH    PLANTS 


discover  if  any  cracks  have  been  formed  which  might 
admit  water  and  so  vitiate  the  results. 

It  is  interesting  to  calculate  the  percentage  of  water 
absorbed  and  make  a  comparison  after  various  periods 
of  immersion. 

The  followinof  will  serve  to  illustrate  the  method:  — 


Twenty-five  Scarlet  Runner 
Beans  sealed 

Twenty- five  Scarlet  Runner 
Beans  unsealed 


Weight  be- 
fore treat- 
ment witli 
i-ubber. 


31.0  grams 
29.5  grams 


Weiglit  after 

treatment 
with  rubber. 


Submerged  in  water 
15  niinuies. 


Wt. 


32.0  grams  32.34 
30.8  grams  31. G2 


Gain. 


0.34 
0.82 


Per 
cent 
gain. 


1.1 

2.8 


Submerged  in  water 
'6b  minutes. 

Submergpd  in  water 
(iO  niinuies. 

Submerged  in  water  1;  Submerged  in  water 
yo  mhiuies.           j|            15  huurs. 

1              1    P^"- 

Wt.    1  Gain.  1   cent 

1              i  gain. 

Wt.      Gain. 

Per 
cent 
gain. 

Wt. 

Gain. 

Per 
cent 
gain. 

Wt. 

Gain. 

Per 
cent 
gain. 

33.30 
32.8 

1.30 
2.0 

4.2 
6  8 

34.45 
.35.2 

2.45 
4.4 

7.9 
15. 

35.69 
39.68 

3.69 

8.88 

11.9 
30.1 

72.71 

24.21 
41.91 

78.1 
142.1 

After  soaking  fifteen  minutes,  the  weight  of  the 
sealed  lot  was  32.34  grams;  subtract  from  this  the 
weight  before  soaking  (32),  which  gives  the  gain 
(0.34  grams) ;  divide  this  by  the  original  weight  be- 
fore treating  with  rubber  (31  grams)  to  get  the  gain 
in  per  cent.  In  this  case  an  area  on  the  unsealed 
seeds  was  covered  with  rubber  so  as  to  equal  the 
amount  covered  on  the  sealed  seeds. 


THIS    AWAKENING    OF    TEE    SEED 


13 


The  experiment  may  be  repeated  in  a  different  form 
by  placing  the  seeds  in  moist  sawdust  instead  of  in 
water.  Care  must  be  taken  that  none  of  the  rubber 
is  removed  in  manipulating  the  seeds. 

This  experiment  requires  a  balance.  If  you  have 
none  at  hand  you  should  make  one  for  yourself.    The 


17.    A  home-made  balance  constructed  of  ximbrella  wire;   it  can  be  made  sensitive 
to  a  tenth  of  a  gram. 

arms  of  the  balance  should  be  of  equal  length.  Why  ? 
Try  the  effect  of  both  equal  and  unequal  arms.  The 
pans  should  be  attached  at  equal  distances  from  the 
pivot.  A  very  good  balance  is  easily  and  quickly 
made  of  umbrella- wire,  as  shown  in  Fig.  17.  The 
long  rib  is  used  for  the  arm  of  the  balance,  the  short 
rib  for  the  support.     The  rivet  is  taken  out  and  a  fine 


14 


EXPERIMENTS    WITH    PLANTS 


needle  substituted  for  it;  the  varnish  is  burned  off  or 
scraped  away.  The  upright  piece  is  firmly  wedged  in 
a  hole  bored  in  a  small  block  of  wood  (see  Fig.  17). 

The  pans  are  made  of  tin  covers, 
attached  with  silk  thread.  Their 
weights  may  be  equalized  by 
trimming  the  edges  or  by  attach- 
ing a  little  sealing-wax  to  them; 
when  balanced  they  should  hang 
about  an  inch  and  a  half  above 
the  table.  Another  kind  of  sup- 
port, made  by  fixing  two  short 
glass  tubes  to  a  strip  of  wood  (by 
means  of  sealing-wax)  is  shown 
in  Fig.  18. 

When  the  balance  is  set  up,  test  it  carefully;  first 
get  the  pans  to  balance;  then  put  weights  in  both 
pans  until  they  balance;  then  exchange  the  weights; 
if  the  balance  is  properly  made  they  should  still 
balance;  failure  to  do  so  shows  that  the  pans  are  not 
of  equal  weight,  or  are  not  attached  at  equal  distances 
from  the  pivot.  An  inaccuracy  in  the  balance  will 
not  vitiate  your  results  for  comparative  purposes  if 
you  always  put  the  weights  in  the  same  pan.  Why? 
If  you  cannot  obtain  weights,  make  some  of  lead 
(to  correspond  with  a  druggist's;  the  metric  system 
is  much  more  convenient  than  the  ordinary  apothe- 
caries' weight). 


THE    A  WAKE^NING    OF    THE    SEED 


15 


It  would  appear  that  considerable  water  enters 
through  the  opening,  the  amount  being  different  in 
different  kinds  of  seeds.  The  question  may  be  raised 
Does  all  the  water  enter  in  this  way?  If,  in  the  ex- 
periment just  concluded,  the  openings  were  securely 
stopped,  it  would  seem  that  we  must,  in  many  cases 
at  least,  answer  negatively.  However,  all  doubt  on 
this  point  may  be  removed  by  partially  submerging 
the  seeds  without  allowing  the  opening  to  come  in 
contact  with  the  water.  A  very  convenient  way  is 
to  place  the  seeds  in  sand  which  is  kept  saturated 
with  water  (see  Fig.  23) :  for  keeping  the  sand  satu- 
rated, the  device  shown  in  Fig.  27  may  be  used.  Or 
we  may  cut  in  a  cork  notches  large  enough  to  receive 
the  seeds;  after  wedging  them  firmly  in  place,  put 
the     cork     in    water 


(Fig.  19).  If  water 
now  enters  the  seed  it 
must  be  through  the 
cover  itself,  since  the 
opening  is  not  in  con- 
tact with  the  water. 
Large,  flat  corks  are 
best;  if  necessary 
they  may  be  obtained 
at  drug- stores.  (Cork  soles  or  the  cork  strips  used  by 
entomologists  are  good.)  Flat  pieces  of  wood  will 
serve    in   place   of  cork.      This   experiment    may   be 


19.    A  method  of  keeping  seeds  half-submerged, 
in  order  to  discover  how  the  water  enters. 


16 


EXPERIMENTS    WITH   PLANTS 


carried  on  by  weighing  in  the  same  way  as  in  the 
previous  one,  and  will  afford  interesting  results  for 
comparison. 

What  seed-covers  admit  water  most  readily?  We 
may  make  a  satisfactory  test  by  splitting  the  covers 
of  dry  seeds  in  halves,  removing  the  germ  and  allow- 


20.  Seed-covers  Hoating  on  water,  each  containing  a  few  sugar  crystals, 
whicli,  by  dissolving,  indicate  the  rapidity  of  osmosis;  controls 
on  the  glass  strip. 

ing  the  dry  covers  to  float  like  boats  on  the  surface 
of  the  water  (see  Fig.  20).  Into  each  put  a  few  crys- 
tals of  sugar,  the  dissolving  of  which  will  indicate 
how  rapidly  water  is  absorbed  through  the  cover.  On 
a  dry  piece  of  glass,  near  the  surface  of  the  water 
but  not  in  contact  with  it,  place  other  boats  contain- 
ing sugar  crystals,  to  see  whether  the  sugar  can  absorb 
enough  moisture  from  the  air  (or  from  the  cover)  to 
dissolve.     In   making  the   boats,   we   must  take   care 


THE    A  WAKENING    OF    THE    SEED  17 

that  there  are  no  openmgs  or  cracks  through  which 
water  can  enter;  be  careful  that  no  water  enters 
the  boat  at  the  rim.  To  imitate  natural  conditions 
more  closely,  place  some  boats  on  the  surface  of  moist 
soil,  pressing  them  down  firmly.  Test  as  many  kinds 
of  seed  as  possible. 

Does  the  germ  (or  endosperm)  possess  the  power  to 
draw  water  through  the  cover  as  the  sugar  does  ?  Repeat 
the  experiment,  substituting  the  ordinary  seed- content 
(either  a  part  or  the  whole)  for  the  sugar:  be  sure 
that  it  is  in  close  contact  with  the  cover.'  Weigh  it 
at  the  beginning  of  the  experiment,  and  repeat  the 
weighing  at  frequent  intervals  to  discover  how  much 
water  it  has  absorbed.  Notice  also  whether  it  softens 
or  appears  moist. 

The  sugar,  when  placed  in  the  boats  as  described 
above,  seems  to  have  the  power  to  draw  the  water 
through  the  seed- cover;  but  if  sugar  were  dissolved 
in  the  water  on  which  the  boats  are  floating,  would  it 
not  exert  a  counter-attraction,  and  tend  to  prevent 
the  water  from  being  drawn^  up  through  the  seed- 
cover?  Prepare  some  boats  (all  from  the  same  kind 
of  seed-cover) ;  place  sugar  in  them  and  float  some 
on  pure  water,  others  on  a  thick  syrup  made  of  sugar 
and  water.  Many  other  substances  besides  sugar  have 
a    strong    attraction   for    water:     the    germ    contains 

1  The  sugar  is  spoken  of  as  drawing  or  attracting  the  water  in  a  popular 
sense  only. 


18  EXPERIMENTS    WITH   PLANTS 

substances  of  this  sort  (salts,  starch,  sugar,  etc.),  and 
we  suppose  that  the  seed  owes  to  them  its  power  to 
absorb  water.  Now  we  have  just  found,  in  the  experi- 
ment with  sugar  in  the  boats,  that  water  is  absorbed 
more  rapidly  than  syrup.  Is  it  so  in  the  case  of  the 
seed  ?  Place  weighed  lots  of  seed  of  the  same  kind  in 
water,  in  syrup  and  in  a  very  strong  solution  of  com- 
mon salt  (dissolve  as  much  salt  as  you  can  in  the 
water).  After  a  day  or  so  remove  the  seeds,  dry 
them  on  the  surface  and  weigh.  Can  you  make  the 
solution  strong  enough  to  prevent  all  absorption  I 
Rinse  the  seeds  in  water  and  plant  them  in  moist 
sawdust,  to  see  whether  the  sugar  or  salt  have  injured 
them  in  any  way. 

Do  you  think  that  the  seeds  will  germinate  in  sea- 
water  ?  If  this  cannot  be  obtained  it  can  be  made 
artificially  by  dissolving  about  3%  per  cent  of  sea- 
salt  (obtainable  at  grocers'  and  druggists')  or  common 
salt  in  water  (4%  drams  of  salt  to  a  pint  or  3X  grams 
to  100  cc.  of  water).  The  seeds  may  be  placed  in  the 
apparatus  shown  in  Fig.  25,  but  cotton  soaked  in  the 
sea- water  is  to  be  substituted  for  the  wire  netting. 
Are  the  seeds  of  plants  which  inhabit  the  seashore 
able  to  germinate  in  sea- water  ?  How  is  it  with  alkali 
soils  in  this  respect  ? 

In  the  boat  experiments  just  described,  we  are 
struck  with  the  fact  that  water  appears  to  come 
through  the  cover  only  where  the  sugar  or  germ  is  in 


THE    A  WAKENING    OF    THE    SEED  19 

contact  with  it.  Is  this  really  the  case,  or  does  the 
water  conae  through  elsewhere,  but  so  slowly  that  it 
evaporates  as  rapidly  as  it  reaches  the  inner  surface 
of  the  cover  ?  Repeat  the  experiment  as  follows : 
Prepare  the  boats  as  before,  and  seal  them  to  strips 
of  glass  by  means  of  sealing-wax,  as  shown  in  Fig.  21. 
Smear  the  rim  of  the  boat  with   hot  sealing-wax,  in 


21.     Modification  of  the  experiment  shown  in  Fig.  20. 

vert  it  on  the  glass  and  run  a  hot  piece  of  wire  around 
the  rim  until  a  tight  joint  is  secured.  Place  the  glass 
(boats  down)  on  a  tumbler,  and  carefully  pour  in 
water  until  it  touches  the  boats;  do  not  let  it  touch 
the  glass  strip.  If  water  enters  the  boats,  moisture 
will  collect  in  drops.  Let  some  of  the  boats  so  treated 
stand  near  by  but  not  in  contact  with  water,  as  a 
control  experiment. 

If,  as  appears  to  be  the  case,  the  water  does  not 
come  through  the  seed-cover  except  where  the  germ 
(or    endosperm)   is    in    contact    with    the    cover    (and 


20 


EXPERIMENTS    WITH  PLANTS 


draws  it  through),  it  would  seem  advisable  to  have  as 
much  contact  as  possible.  Some  seeds  have  the  cover 
closely  applied  to  the  germ  so  as  to  be  in  contact 
everywhere;  others  (Peanut,  Filbert,  etc.),  wiiere  the 
seed-contents  are  loose  inside  the  cover,  have  a  small 
amount  of  contact;  investigate  this  point  in  as  many 
seeds  as  you  can.  In  some  seeds  the  cover  separates 
in  places  from  the  germ  when  the  seed  is  placed  in 
water,  so  that  the  amount  of  contact  is  diminished; 
subsequently  the  cover  becomes  closely  stretched  over 
the  germ ;  in  what  seeds  does  this  happen  ? 

It  would  seem  that  the  portion  of  the  germ  which 
is  in  immediate  contact  with  the  opening  must  receive 
water  more  quickly  and  in  larger  quantities  than  other 
parts  more  remote.     Do  you  usually  find  the  caulicle 

near  the  opening?^  Does  the 
caulicle  usually  swell  and  grow 
more  quickly  than  other  por- 
tions of  the  seed  ?  Do  you 
consider  its  position  advanta- 
geous ?  Notice  the  pocket 
around  the  caulicle  in  the 
Beans  (Fig.  22),  Pea,  Buckeye 
(Fig.  46),  etc.  Do  you  think 
this  might  help  to  draw  up 
water  (by  capillarity)  and  retain  it,  so  keeping  the 
caulicle  moist? 


22 


Scarlet  Runner  Bean  opened, 
showing  tlie  pocket  into  which 
the  caulicle  fits. 


1  Examine  particularly  the  Peach,  Plum,  Cherry,  Walnut,  Pecan,  etc. 


THE    A  WAKENING    OF    THE    SEED 


21 


Not  only  is  it  important  that  the  germ  should  be 
in  contact  with  the  cover,  but  also  that  the  cover 
should  be  in  close  contact  with  the  soil.     Hence  the 


23.     Seeds  half-submerged  in  wet  sand,  to  determine  how  the  water  enters. 

necessity  of  rolling  the  soil  to  pack  it  firmly  about  the 
seeds  as  practiced  by  farmers,  and  "firming"  the  soil 
about  the  seeds  as  practiced  by  gardeners,  i.  e.,  by 
covering  the  seeds  and  then  treading  on  them  or  by 
pressing  down  the  soil  with  a  board. 

Since  the  opening  is  so  important,  it  may  be  that 
its  position  with  reference  to  the  soil  may  be  impor- 
tant when  the  seed  lies  on  the  surface.  On  the  sur- 
face of  the  soil  in  some  pots  (or  boxes)  place  some 
seeds,  one-third  with  the  opening  up,  one-third  with 
the  opening  down,  one -third  flat  on  the  soil  (see  Fig. 
23).  Press  all  seeds  firmly  into  the  soil,  so  that  each 
one  is  just  half- buried.  Which  germinate  first  ?  Corn 
gives  very  striking  results  (Fig.  23  a).  Does  the  nat- 
ural position  of  the  seed  on  the  soil  usually  bring  the 
opening  in  contact  with  the  earth  ?     Do  you  see  any 


22 


EXPERIMENTS     WITH    PLANTS 


advantage  in  having  the  seed  flattened  ?  In  a  flat- 
tened seed,  what  is  the  best  position  for  the  opening  ? 
Where  is  the  opening  usually  found  in  a  flattened 
seed? 

What  course  does  the  water  take  after  entering  the 
seed  ?  Perhaps  the  best  way  to  trace  the  path  of  the 
water  is  by  dissolving  some  coloring  matter  in  it. 
Eosin  (obtainable  as  Eosin  Pink,  one  of  the  Diamond 

\ 


23a 


Three  idws  of  Corn  planted  at  the  same  time,  each  grain  being 
half-buried  in  the  moist  soil:  those  in  the  first  row  were  placed 
flat  on  the  surface;  those  in  the  second  row  with  tlie  pointed  end 
upward;  those  in  the  last  row  with  the  pointed  end  downward. 


THE    AWAKENING    OF    THE    SEED 


23 


Dyes,  at  drug- stores)  or  ordinary  red  ink  answers  ad- 
mirably. Dissolve  enough  in  water  to  make  it  bright 
red,  and  then  submerge  the  seeds  in  the  solution;  it 
is  well  to  use  a  good  many  seeds  and  to  remove 
some  every  few  minutes  and  take 
off  the  covers  to  see  how  far  the 
water  has  penetrated. ^  Do  you 
find  that  the  water  penetrates  first 
at  the  opening  ?  In  what  direction 
does  it  spread  inside  the  seed? 
What  external  indications  do  you 
see  of  this  in  the  Bean  (Fig.  14)? 
Trace  it  with  especial  care  in  the 
Walnut  and  Pecan.  Although 
in  these  nuts  the  contact  between 
the  germ  and  the  cover  is  small, 
yet  this  is  offset  by  an  absorb- 
ent, wick- like,  central  strand  which  takes  up  water 
directly  from  the  opening  and  from  which  water 
spreads  out  into  the  broad  partitions  which  are  in  con- 
tact with  the  folds  and  surfaces  of  the  germ;  the 
caulicle  lies  at  the  end  of  the  fibrous,  wick -like  strand 
(Fig.  24). 

We  shall  probably  find  that  the  coloring  matter 
will  not  penetrate  into  the  germ,  although  the  water 
does;  the  method  is  only  trustworthy  as   showing  the 

1  The  seed  should  be  washed  and  wiped  with  a  cloth  to  remove  the  dye. 
Eosin  stains  may  be  removed  from  hands  and  colorless  fabric  by  Javelle  water 
(obtainable  at  druggists')  or  by  bleaching  powder  (obtainable  at  grocers' J. 


Walnut  divided  in  half, 
showing  the  wick-like,  cen- 
tral strand  (s)  by  which  the 
water  travels  through  the 
seed  to  the  caulicle  and  the 
broad  absorbent  plates  by 
means  of  which  it  spreads. 


24  EXPERIMENTS    WITH   PLANTS 

path  of  the  water  to  and  around  the  germ  and  endo- 
sperm, but  not  into  it. 

In  most  of  the  thick  covers  (Filbert,  Walnut, 
Pecan,  Peach,  etc.)  we  shall  find  that  the  water  pur- 
sues special  paths  in  the  tissue  of  the  cover.  -  These 
represent  the  paths  which  the  sap  took  while  the  fruit 
was  still  attached  to  the  plant.  It  will  prove  interest- 
ing to  obtain  young  fruits  of  various  kinds  and  place 
the  cut  surface  of  the  stem  in  eosin  solution,  to  trace 
the  path  taken  by  the  sap. 

It  may  prove  interesting  to  raise  the  question.  Is 
not  the  seed-cover  (in  spite  of  the  opening)  a  serious 
hindrance  in  absorbing  water?  We  may  answer  this 
by  removing  the  covers  from  some  seeds  and  placing 
them  in  water  (together  with  the  untreated  seeds  for 
comparison).  Select  ten  lots  of  seeds  (twelve  in  each 
lot)  free  from  cracks,  etc.  Remove  the  covers  from 
one  lot  and  then  weigh  each  lot  separately.  Sub- 
merge them  all  in  water,  keeping  the  different  lots 
separate.  After  half  an  hour  remove  one  of  the 
untreated  lots;  take  off  the  covers  and  weigh.  Let 
the  covers  stand  until  "air- dry,"  and  then  weigh 
them.  Deduct  this  weight  from  the  original  weight 
of  this  particular  lot;  this  will  give  us  approximately 
the  original  weight  of  the  seed-contents  (i.e.,  the 
seed  minus  its  covers).  We  now  know  approximately 
how  much  the  seed  -  contents  weighed  at  the  start, 
also  how  much  they  have  gained.  We  may  compare 


:}^<>'* 


THE    A  WA  KENINO    OF    TEE    SEED  25 

this  with  the  gain  of  the  seeds  which  were  deprived 
of  their  covers  at  the  start.  After  another  half  an 
hour,  remove  another  lot  and  weigh;  repeat  this  each 
half- hour.  Any  seeds  may  be  used;  it  would  seem 
desirable  to  test  some  which  have  thin  covers  (Bean, 
etc.)  and  some  which  have  thick  covers  (Filbert, 
Peach,  etc.). 

If  you  can  obtain  seeds  of  the  Moonfiower,  Mexican 
Morning-glory  or  Lupine,  the  weighing  will  be  un- 
necessary; the  results  will  be  sufficiently  striking  to 
the  eye   to  leave  no  room  for  doubt. 

Nurserymen  recognize  that  the  covers  of  many 
seeds  (e.  g..  Peach  pits,  etc.)  are  a  hindrance  to 
germination,  and  before  planting  them  usually  crack 
the  cover;  other  seeds  have  the  covering  cut  by  a 
knife  or  file,  while  still  others  are  mixed  with  sand 
and  rubbed  or  pounded.  Acacia  seeds  are  boiled 
for  ^YQ  or  ten  minutes,  which  aids  the  penetration 
of  water  through  the  hard  coat  and  makes  a  difference 
of  months  in  the  germination,  while  some  kinds  are 
placed  in  boiling  water  and  allowed  to  cool  slowly.^ 

How  much  water  is  necessary  for  germination?  We 
may  get  an  approximate  answer  to  this  question  by 
taking  several  pots  of  the  same  size,  filling  them  with 
dry  sand  and  placing  in  each  twelve  seeds  (the  same 
sort  in  each  pot).  Water  the  pots  regularly,  giving 
to  No.  1   a  very   small   quantity  of  water  each  time, 

'  The  heat  may  have  an  important  stimulating  effect. 


26 


EXPERIMENTS    WITH   PLANTS 


to  No.  2  twice  as  much  as  to  No.  1,  to  No.  3  twice  as 

much  as  to  No.  2,  and  so  on. 

Another  method   is  to  use  fruit -jars   (one -quart  or 

two-quart),   placing  the   seeds  on  the   bottom   of  the 

jar  and  covering  them  with  half  an  inch  of  sand.    Add 

different  quantities  of  water  to 
the  different  jars,  and  screw  on 
the  tops  tightly. 

Whichever  method  be  used, 
it  is  interesting  to  determine 
the  amount  of  water  in  the 
seed  at  the  stage  when  the  cau- 
licle  begins  to  protrude.  This 
may  be  ascertained  by  weigh- 
ing the  seed  and  then  drying  it 
(on  a  water-bath;  see  Fig.  54) 
until  it  ceases  to  lose  weight; 
dividing  the  loss  in  weight  by 
the  weight  of  the  undried  seed 
will  give  the  percentage.  The 
determination  is  especially  in- 
teresting  in   the    case    of    the 

seeds  which  germinate  with   the  minimum  amount  of 

moisture. 

It  often  happens  that  a  seed  has  little  or  no  water 

at  its  disposal  except  the  moisture  of  the  air.     Unless 

it  can  absorb  this  in   sufficient  quantities,   it  cannot 

germinate. 


Seeds  placed  in  a  saturated 
atmosphere. 


THE    A  WAKENING    OF    THE    SEED 


27 


Another  method  of  keeping  seeds 
in  a  saturated  atmosphere. 


The  question  may  be 
raised,  Can  seeds  absorb 
enough  water  from  moist  air 
alone  to  enable  them  to  ger- 
minate? This  may  be  an- 
swered by  placing  some  seeds 
in  a  saturated  atmosphere 
for  a  time.  Place  the  seeds 
in  a  fruit-jar,  supported  on 
a  piece  of  wire  netting,  as 
shown  in  Fig.  25.  Place  a 
little  water  in  the  bottom  of  the  jar  and  screw  the 
cover  on  tight.  Drops  of  condensed  mois- 
ture are  not  apt  to  fall  on  the  seeds  when 
a  fruit- jar  is  used, 
but  should  this 
happen  start  the 
experiment  over 
again,  protecting 
the  seeds  by  a 
small  inverted 
cone  of  wire  net- 
ting or  a  small 
glass  funnel.  The 
apparatus  shown 
in  Fig.  26  may  also 
be  used:   vaseline 

i«  ncoH  fr.  mol^ck  on        ^^-    '^^^^^^  ^f  maintaining  a  saturated  atmosphere 
lb  USea  to  maKe  an  ^nd  a  constant  water-level. 


28  liXPElilMENTS     WITH    PLANTS 

air-tight  joint  with  the  glass  cover.  The  apparatus 
shown  in  Fig.  27  is  very  convenient  for  this  purpose: 
the  inverted  bottle  has  a  cork  in  the  sides  of  which 
two  grooves  are  cut,  so  that  as  soon  as  the  water  sinks 
below  the  mouth  of  the  bottle  air  enters  through  the 
grooves  and  water  runs  out  until  the  level  rises  and 
closes  the  grooves:  the  water-level  thus  remains 
almost  constant. 

As  the  experiment  is  to  last  for  some  time,  it  is 
advisable  to  take  precautions  against  the  growth  of 
mould.  Place  the  seeds  in  a  tumbler  and  set  them  in 
a  jar  or  pail  in  the  bottom  of  which  is  a  little  forma- 
lin: cover  the  pail  so  as  to  confine  the  formalin  vapor, 
and  let  it  stand  five  or  six  hours. 

Control  seeds  (treated  in  the  same  way)  should  be 
planted  in  moist  earth  or  sawdust. 

The  experiment  should  be  continued  two  or  three 
months  if  necessary.  The  percentage  of  moisture  in 
the  seeds  may  be  determined  at  the  beginning  and 
again  at  the  end  of  the  experiment,  to  see  how  much 
moisture  they  have  absorbed  and  also  the  minimum 
amount  which  will  enable  the  seed  to  germinate. 

The  power  to  absorb  water  from  moist  air  may  be 
of  great  practical  importance  in  storing  seeds,  etc., 
since  if  kept  in  a  damp  place  they  may  easily  germi- 
nate or  decay. 

Of  especial  interest,  in  considering  the  absorption 
of  water,  are  the  mucilaginous  covers  of  Flax,  Quince, 


THE    AWAKENING    OF    THE    SEED  29 

Radish,  Squash,  etc.  Such  covers  can  absorb  a  large 
amount  of  water  even  in  a  passing  shower  and  hold 
it  after  the  surrounding  earth  is  again  dry.  Many 
seeds  have  spongy  covers  which  act  in  much  the  same 
way,  as,  for  example,  the  Walnut,  Hickory,  Almond 
(in  which  cases  the  spongy  cover  is  usually  removed 
before  the  nuts  come  to  market).  Nasturtiums,  etc. 
The  Walnut  (Fig.  24),  Hickory  and  Pecan  have  a 
central,  wick -like  strand  of  absorptive  tissufe  which 
conveys  the  water  directly  to  the  germ,  over  the  sur- 
face of  which  it  is  spread  out  in  a  thin  layer  by  means 
of  thin  plates  of  absorptive  tissue.  In  the  grasses 
and  grain-plants  the  seeds  are  surrounded  by  parts  of 
the  flower  (the  "chaff"),  which  assist  greatly  in  soak- 
ing up  and  retaining  moisture,  while  the  pulp  of  soft 
fruits  and  berries  serves  the  same  purpose.  In  the 
Castor- bean  (Fig.  3)  the  large,  spongy  outgrowth  at 
one  end  (caruncle)  serves  the  same  purpose,  as  can 
be  shown  by  planting  Castoi -beans  dt-'prived  of  the 
caruncle  alongside  of  unmutilated  ones;  its  position  is 
such  that  the  water  passes  from  it  directly  through  the 
opening  to  the  radicle,  and  it  will  be  noticed  that  the 
germ  is  attached  to  the  cover  only  at  this  one  point. 

We  have  now  found  out  something  about  how  the 
seed  gets  water,  and  we  can  see  clearly  that,  while 
the  need  is  the  same  in  all  cases,  the  means  adopted 
by  different  plants  to  supply  this  need  are  various; 
in  other  words,  the  same  problem  is  solved  in  a  variety 


30 


EXPERIMENTS    WITH   PLANTS 


of  ways.  Perhaps  we  cannot  say  in  all  eases  which 
solution  is  the  best:  certainly,  in  absorbing  water  the 
thinnest  and  most  permeable  cover  is  the  best,  but 
whether  such  a  cover  would  in  all  cases  furnish  suf- 
ficient protection  to  the  seed  before  germination  we 
cannot  tell  without  a  special  study  of  that  question. 

We  know  that,  besides 
water,  air  is  needed.  How 
does  the  germ  get  air  ?  Does 
air  pass  readily  through  the 
seed -cover?  We  may  find 
out  by  sealing  the  cover 
(air-tight)  to  one  end  of  a 
glass  tube,  filling  the  tube 
with  water  and  inverting  it, 
as  shown  in  Fig.  28,  in  a 
glass  of  water,  taking  care 
not  to  admit  any  air  into 
the  tube;  the  water  should 
be  boiled  just  before  using, 
in  order  to  expel  the  air. 
To  seal  the  tube  to  the 
cover,  smear  the  end  of  the 
tube  liberally  with  hot  sealing-wax;  remove  the  super- 
fluous wax  from  the  interior  of  the  tube,  press  the  end 
of  the  tube  firmly  against  the  cover  (which  must  be 
free  from  cracks  or  openings),  and  run  a  hot  wire 
around  it  until  a  tight  joint  is  secured;   allow  the  wax 


28.     Method  of  testing  the  permeability 
of  the  seed-cover  to  air. 


THE    A  WAKE XI NO    OF    THE    SEED  31 

to  harden,  then  test  the  joint  by  placing  the  sealed  end 
of  the  tube  under  water  and  blowing  into  it  forcibly. 

The  weight  of  the  water- column  tends  to  draw  air 
through  the  cover.  If  any  air  enters  it  will  appear  as 
a  bubble  at  the  top  of  the  tube;  should  this  happen, 
empty  the  tube  and  test  the  joint  as  before  by  blow- 
ing forcibly.  If  no  leak  is  detected,  refill  the  tube 
and  invert  it  as  before.  Test  different  sorts  of  seeds, 
especially  those  whose  covers  seem  most  porous  and 
permeable  to  air.  It  should  be  remembered  that  in 
this  case  we  are  testing  a  seed -cover  which  is  in  con- 
stant contact  with  water;  peihaps  in  a  dry  condition 
it  would  admit  more  air.  This  may  be  tested  by  fill- 
ing the  tube  only  partly  full,  so  as  to  leave  a  large 
air- bubble  at  the  top  of  the  tube;  mark  its  limit 
exactly  on  a  piece  of  paper  pasted  on  the  outside  of 
the  tube;  the  entrance  of  air  can  then  be  detected  by 
the  increase  in  the  size  of  the  bubble.  We  may,  if  we 
wish,  avoid  any  contact  of  water  with  the  cover,  by 
sealing  on  a  cover,  warming  the  tube  well  and  placing 
the  unsealed  end  in  water  ;  as  the  air  in  the  tube 
cools,  water  will  be  drawn  in.  Which  of  these  tln^ee 
methods  approximates  closest  to  the  condition  of  the 
cover  during  germination  ? 

Does  air  enter  the  seed  through  the  openings?  You 
may  test  this  matter  by  closing  the  openings  of  seeds 
which  have  been  previously  thoroughly  soaked  (in 
order    to    ensure    a    sufficient    supply    of    water    for 


32  EXPERIMENTS     WITH   PLANTS 

germination)  and  placing  them  in  an  atmosphere  satu- 
rated with  water  (to  prevent  them  from  losing  any 
water),  together  with  untreated  seeds  as  control.  The 
openings  may  be  closed  and  tested  as  described  on 
page  10. 

The  seeds  may  be  placed  on  wire  netting,  in  a  fruit- 
jar  containing  water,  as  shown  in  Fig.  25  (the  cover 
must  be  tightly  screw^ed  on) .  At  least  a  dozen  seeds 
should  be  treated  and  the  same  number  used  as  a 
control.  The  precautions  against  mould  mentioned 
on  page  28  should  be  observed.  Set  the  jar  in  a 
place  warm  enough  to  promote  germination.  If  the 
seed  depends  largely  upon  the  opening  for  the  admis- 
sion of  air,  we  shall  expect  to  find  the  germination  of 
the  treated  seeds  noticeably  delayed. 

How  much  air  is  necessary  for  germination?  We 
may  get  an  approximate  idea  by  taking  six  bottles  of 
the  same  size  and  filling  them  to  various  heights  with 
moist  sand,  as  shown  in  Fig.  29  (the  first,  one- sixth 
full;  the  second,  two-sixths,  etc.).  To  exclude  air 
from  the  sand,  the  bottle  may  be  first  filled  with  water 
and  the  dry  sand  slowly  poured  into  it  to  the  desired 
height;  the  superfluous  water  may  then  be  poured 
off.  The  seeds  (well  soaked)  may  then  be  put  in  (the 
same  number  in  each  bottle),  the  cork  may  then  be 
pushed  down  below  the  rim  and  sealed  air-tight  with 
vaseline  or  sealing-wax.  A  closer  approximation  to 
the  correct  amount  could  easily  be  made  if  the  experi- 


TnE    AWAKENING    OF    THE    SEED 


33 


ment  were  to  be  repeated  and  the  bottles  filled  more 
nearly  to  the  right  degree  at  the  start.  We  may  vary 
the  experiment  by  dispensing  with  the  sand  and  simply 
filling  up  the  bottles  to  various  heights  with  soaked 
seeds. 

The   fact  that   so  much  air  is  necessary   seems   to 
indicate    that    some    part  of   the   air   is   changed    (or 


29.     Seeds  on  wet  sand  with  different  amounts  of  air  at  their  disposal. 

"used  up")  by  the  seeds.  Let  us  see  if  this  is  so. 
After  two  or  three  days,  cautiously  remove  the  cork 
from  one  of  the  bottles  (.containing  about  five -sixths 
air)  and  immediately  lower  a  lighted  match  into  it; 
or,  better  still,  take  a  tall  bottle  or  jar,  place  a  layer 
(an  inch  or  so  deep)  of  seeds  in  the  bottom,  stopper 
tightly,  allow  it  to  stand  a  day  or  so  and  test  with 
lighted  match.  If  the  match  goes  out,  it  indicates 
that  the  oxveen  of  the  air  has  united  with  some  other 


34 


EXPElUMKXTt^    WITH   PLANTS 


substance  so  that  it  no  longer  supports  combustion. 
We  may  now  pour  a  little  lime-water  into  the  jar, 
replace  the  stopper  and  shake  vigor- 
ously. (Lime-water  is  prepared  by 
placing  a  little  unslaked  lime  in  a 
metal  dish  or  pail,  filling  the  pail 
with  water  and  allowing  it  to  stand 
for  a  day;  the  water  should  then 
be  filtered  through  filter- paper  or 
through  a  cotton  plug  in  the  neck 
of  a  funnel.)  If  the  lime-water 
turns  milky,  it  indicates  that  the 
oxygen  has  united  with  the  carbon 
of  the  plant  to  form  carbon  diox- 
ide, a  gas  familiar  to  us  as  soda- 
water  gas.  Arrange  an  experiment,  as  shown  in  Fig. 
30,  by  placing  a  vial  of  clear 
lime  -  water  surrounded  by 
soaked  seeds  in  a  jar  and  stop- 
pering loosely.  As  a  control, 
use  a  similar  arrangement 
without  the  seeds.  We  may 
make  use  of  the  fact  that  car- 
bon dioxide  is  readily  absorbed 
by  lye  to  perform  a  further  ex- 
periment.   Arrange  two  bottles 

31.  Method  of  measuring  the  amount 

(pint  or  half -pint),  as  sliown        ^L^'S^'',°.?„/St  fhet^^w '^ 
in  Fig.  31,  by  fitting  them  with        J.^,'?)"  "'  *''°"'"'  "  "^ 


30.  Apparatus  for  deterniin- 
ing  whether  germinating 
seeds  produce  carbon  diox- 
ide, the  vial  is  filled  with 
lime-water.  (.Seen  in  sec- 
tion.) 


THE    AWAKENING    OF     THE    SEED  35 

rubber  stoppers  or  cork  stoppers  which  have  been 
soaked  in  melted  paraffin  (obtainable  at  grocers' ;  we 
may  also  obtain  it  in  the  form  of  paraffin  candles). 
Pierce  the  stoppers  with  closely  fittiDg  glass  tubes 
long  enough  to  reach  nearly  to  the  bottom  of  the 
bottle.  Place  seeds  in  one  bottle  to  the  depth  of  an 
inch;  leave  the  other  bottle  empty.  Support  both 
in  an  inverted  position  (by  means  of  clothes-pins  and 
rubber  bands  or  wire,  as  shown  in  the  figure),  allow- 
ing the  tubes  to  dip  into  a  strong  solution  of  lye.  As 
the  carbon  dioxide  is  formed  it  will  be  absorbed  by 
the  lye,  which  will  rise  in  the  tube  and  thus  indicate 
the  amount  produced. 

When  carbon  unites  with  oxygen  we  say  that  it 
burns.  Whether  we  burn  wood,  coal,  oil  or  alcohol, 
the  principal  combustible  substance  is  the  carbon, 
which,  by  uniting  with  the  oxygen,  produces  carbon 
dioxide  and  sets  free  heat.  The  heat  of  our  bodies  is 
due  to  the  same  process  of  burning  and  the  carbon 
dioxide  is  given  off  in  the  breath,  as  is  easily  shown 
by  placing  one  end  of  a  tube  under  lime-water  and 
blowing  into  it.  The  carbon  of  the  body  burns,  but 
it  does  so  very  slowly.  In  the  seed  the  process  is  still 
slower.  The  slight  degree  of  heat  set  free  can  be  meas- 
ured by  carefully  comparing  two  thermometers  (by 
placing  them  side  by  side  in  water  at  various  tempera- 
tures and  comparing  their  readings)  and  then  arranging 
them  as  shown  in  Fig.  32.     One  tumbler  is  filled  with 


36 


EXPERT  ME  XTS    WITU   PLANTS 


soaked  seeds,  the  other  with  moist  cotton  (to  make  the 
conditions  equal  so  far  as  evaporation  is  concerned), 
and  a  piece  of  cardboard  is  laid  over  the  top.  The 
thermometers  are  inserted  to  equal  depths  and  read- 
ings are  taken  every  fifteen  minutes.  A  difference  of 
more  than  a  degree  is  not  to  be  expected  in  most 
cases  and  it  is  often  less  than  this.  The  tumblers 
must  not  be  placed  in  the  sunlight. 

How  do  seeds  get  air  under  ground?  Does  the  soil 
contain  air?  Fill  a  bottle  just  half-way  to  the  neck 
with  the  soil  to  be  tested;    place  a  thin  layer  of  wet 


THE    AWAKENING    OF    THIS    HEED 


37 


I 


V: 


33.  Method  of  determining 
whether  air  exists  in  the 
soil. 


mM 


soil  on  top  of  it  and  tamp  it  down  well  with  the  blunt 

end  of  a  lead-pencil;   fill  the  bottle  to  the  neck  with 

water  so  that  the  spaces  occupied  with  water  and  soil 

are  about  equal  (the  tamped-down 

layer  is  to  prev^ent  the  water  from 

penetrating  the  soil  before  we  are 

ready).      Insert    a    cork    pierced 

with  a  wire  (as.  shown  in  Fig.  33) 

and  force  the  wire  down  so  as  to 

puncture  the  tamped  layer  (move 

it  from   side  to  side   if  necessary 

until  the  air  begins  to  bubble  up) . 

When  the  air  has  all  risen,  we  can 

tell  approximately  how  much  was 

contained  in  the  soil. 

When  the  method  is  under- 
stood, we  may  dispense  with  the 
cork  and  tamped-down  layer  and 
proceed  as  follows :  Take  two  bot- 
tles of  the  same  inside  diameter; 
fill  both  to  the  same  height  (half-full  or  less),  one 
with  water,  the  other  with  the  soil  to  be  tested;  pour 
the  soil  slowly  into  the  bottle  containing  water.  If 
the  soil  contains  no  air  it  should  cause  the  level  of 
the  water  to  rise  to  just  twice  the  height  at  which 
it  stood  originally;  the  amount  by  which  it  fails  to  do 
this  measures  the  amount  of  air  in  the  soil.  The 
result  depends  somewhat  on  how  tightly  the  soil  was 


38  j^xPEiiiMKyrs   with  plasts 

packed  in  the  bottle  at  first.  The  natural  condition 
of  the  soil  could  be  more  closely  simulated  by 
forcing  a  tin  cylinder  (a  tin  can  with  the  bottom 
removed  would  do)  into  the  soil  (using  a  rotary  mo- 
tion) ,  measuring  the  cylinder  of  soil  so  obtained  and 
pouring  it  slowly  and  carefully  into  an  equal  bulk 
of  water. 

The  deeper  the  seed  lies  in  the  soil,  the  less  will 
be  the  circulation  of  air  about  it.  A  constant  renewal 
of  air  is  necessary,  as  we  have  already  learned.  The 
question  naturally  comes  up,  How  does  the  depth  at 
which  the  seed  is  buried  affect  germination  ?  One  way 
of  finding  out  is  by  means  of  a  box,  with  one  side 
of  glass,  in  which  seeds  may  be  planted  at  different 
depths,  as  shown  in  Fig.  34.  A  convenient  way  of 
making  such  a  box  is  to  prepare  the  sides  (as  shown 
in  the  figure)  and  then  make  saw  cuts  in  them  to 
receive  the  glass,  which  is  then  easily  removed  when- 
ever necessary.  A  wooden  strip  for  the  bottom  and 
another  for  the  side  (to  give  rigidity)  complete  the  box. 
Both  sides  may  be  of  glass,  or  one  of  glass  and  the 
other  of  wood.  A  box  an  inch  wide  at  the  top,  with 
sides  a  foot  square,  is  of  very  convenient  size.  The 
joints  may  be  made  air-tight  by  means  of  putty. 
In  planting  the  seeds,  the  box  should  be  tilted  and 
a  row  of  seeds  placed  directly  on  the  glass;  earth 
should  then  be  pressed  down  on  them;  another  row 
of  seeds  should  then  be  planted,  and  so  on  until  the 


THE    A  WAKENING    OF    THE    SEED 


39 


top  is  reached.  The  box  should  then  be  filled  with 
earth  and  the  last  row  of  seeds  planted  on  the  top. 

The  soil  should  be  kept  moderately  moist  and 
at  a  temperature  favorable  to  germination.  The  seeds 
are  now  under  approximately  the  same  conditions  as 
exist  in  the  soil;  as  we  go  deeper  we  find  more  water, 
less  air  (and  less  circulation  of  air)  and  less  warmth 
(in  our  apparatus  the  lower  layers  of  soil  are  apt  to  be 
warmer  than  is  naturally  the  case).  Our  experiment 
indicates  that  there  is  a  certain  depth  where  the  three 
needs  of  the  germinating  seed  are  best  provided  for. 

Various  mechanical  devices  are  in  use  for  planting 
seeds  at  uniform  depths  in  the  soil  (e.  g.,  corn-plant- 


34.     Apparatus  for  determining  how  deep  seeds  sliould  be  planted 


40  EXPERIMENTS    WITH  PLANTS 

ers,  etc.).     In  sowing  seed  in  the  garden,  the  simplest 
and   most  effective  way  is  to  press  a  board   edgewise 

into  the  soil  to  the  right 
depth,  place  the  seeds 
in  the  depression,  fill  it 
with  earth  and  pack  it 

A  planting  stick,  to  secure  uniform  depth      fil'^lly      by     prCSSing     thC 
in  planting  seeds.  j^^^g^^.^^   ^^^^  ^^^^  ||.^        ^ 

board   such   as   is    shown  in  Fig.  35  may   be  used  to 
secure  a  uniform  depth. 

The  circulation  of  air  in  the  soil  will  depend  on  the 
way  in  which  it  is  packed  in  the  box,  on  the  condition 
of  the  surface  (whether  a  crust  forms  or  not),  on  the 
kind  of  soil  used  and  on  the  amount  of  moisture  in 
the  soil.  It  will  be  found  worth  while  to  vary  the 
conditions  by  filling  one  box  with  sand,  another  with 
clay  and  another  with  a  mixture  of  equal  parts  of  sand 
and  old  loam,  which  makes  a  very  excellent  soil  for 
seeds.  Water  the  boxes  equally  throughout  the  ex- 
periment. Gardeners  always  recognize  the  necessity 
for  "good  drainage"  (i.  e.,  proper  circulation  of  air 
in  the  soil),  and  secure  it  in  a  variety  of  ways.  The 
seeds  are  usually  sown  in  shallow  boxes,  porous  earthen 
dishes,  or  in  ordinary  pots,  in  which  case  a  layer  of 
pebbles  or  pieces  of  broken  pots  is  placed  in  the  bot- 
tom. The  surface  of  the  soil  is  protected  from  baking 
(which  forms  a  crust)  by  a  cover  of  sawdust  or  litter, 
or  by  being   shaded;    the   shade   is   also   of  value  in 


THE    AWAKENING    OF    THE    SEED  41 

protecting  the  seeds  from  drying.  A  screen  made  of 
lath  or  brush,  as  shown  in  Fig.  36,  affords  an  excel- 
lent means  of  shading  a  seed-bed;  a  screen  of  muslin 
cloth  is  very  commonly  used. 

The  quality  of  the  soil  should  be  carefully  attended 
to.  It  should  be  of  such  consistency  that  it  will  pack 
firmly  around  the  seeds  but  will  not  bake  into  a  hard 
crust:  a  mixture  of  sand  and  good  garden  loam  in 
equal  quantities  usually  makes  a  good  soil  for  this  pur- 
pose. In  some  cases  moss  or  cocoanut  fiber  is  used 
instead  of  soil. 

Very  small  seeds  are  sown  on  the  surface  of  the  soil, 
which  has  been  sifted  and  then  carefully  smoothed. 
They  must  then  be  protected  against  drying  up  by  a 
glass  frame  placed  over  them,  or  sometimes  by  a 
board  laid  over  them:    after  they  have  germinated. 


36.     Screens  for  seed-beds;  a  brush  screen  on  the  left,  a  lath  screen  on  the  right. 

the  board  is  replaced  by  a  piece  of  glass  raised  an 
inch  or  so  above  the  soil. 

In  some  cases  such  seeds  are  covered  with  fine 
moss.  In  sowing  grass  seeds  for  lawns,  it  is  very 
desirable  to  cover  the  seeds  with  stable  manure  or 
straw.     Such  a  covering  not  only  keeps  the  seeds  from 


42 


EXPERIMENTS    WITH   PLANTS 


drying  up  but  prevents  them  from  being  washed  away 
in  watering.  In  watering  small  seeds  where  no  such 
covering  is  used,  a  cloth  may  be  laid  over  them  or 
water  may  be  applied  to  the  soil  from  below  (by  set- 


f{ 


!<? 


ting  the  box  ov  pot  in  water  for  a  short 
time) . 

Is  it  possible  to  prevent  germination 
by  keeping  the  soil  too  wet  (i.  e.,  by 
excluding  air  by  water)  ?  Would  a  reser- 
voir of  air  in  the  seed  be  useful  in  very 
wet  soil  ?  Peanuts  and  Castor-beans  are 
said  to  rot  in  wet  soil  if  their  coats  be 
removed,  but  not  otherwise;  do  you  see 
why  this  may  be  true!  Try  planting 
them  (with  the  coats  both  off  and  on) 
in  pots  of  earth  which  are  allowed  to 
stand  in  pans  of  water. 

How  does  the  seed  absorb  warmth? 
Is  the  seed -cover  a  hindrance  in  this 
respect  also?  Seal  the  bulb  of  a  ther- 
mometer into  a  seed- cover,  as  shown  in 
Fig.  37  (first  removing  the  contents  of 
the  seed) .  Place  this,  together  with  a 
naked  thermometer,  which  has  first  been 
carefully  compared  with  it,  on  the  surface 
of  the  soil  in   sunlight  (thus  imitating 


37.  Method  of  testing    thc  couditlou  of  a  sccd  so  placed) ;  take 

the  permeabihty  or  a  /    / 

the    seed  -  cover   to 

heat. 


readings  every  ten  or  fifteen  minutes. 


THE    A  WAKENING     OF    THE    SEED  43 

Place  the  bulbs  of  both  thermometers  equally 
deep  (from  half  an  inch  to  an  inch  and  a  half)  under 
the  surface  of  the  soil  (thus  imitating  the  condition  of 
a  buried  seed),  and  take  readings  as  before  (the 
soil  should   be  placed  in  the  sunlight) . 

Place  both  thermometers  at  the  same  distance  from 
a  sheet  of  hot  metal  (or  a  stove  or  steam  radiator), 
and  take  readings. 

Heat  both  until  they  stand  at  the  same  tempera- 
ture (100°  to  150°  F.),  and  then  place  them  in  a  cool 
place,  to  see  which  loses  heat  more  rapidly. 

Test  several  kinds  of  seeds  in  this  way. 

Does  wetting  the  seed- cover  make  any  difference? 

What  kinds  of  soil  absorb  warmth  (from  the  sun) 
most  rapidly  ?  What  kinds  retain  it  longest  ?  Does 
the  amount  of  moisture  in  the  soil  affect  this  ?  Devise 
an  experiment  to  answer  this  question. 

We  have  learned  something  about  the  awakening 
of  the  seed,  but  there  are  still  many  questions  of 
interest.  How  soon  can  the  seed  awaken?  Try  im- 
mature seeds  to  see  if  they  will  germinate,  especially 
seeds  of  Tomato,  Wheat  and  Barley.  (Rain  at 
harvest- time  often  causes  grain  to  sprout  in  the  ear. 
Seeds  from  half -grown  green  Tomatoes  are  used  by 
some  gardeners  for  special  purposes.  Plants  from 
such  seeds  give  earlier  and  larger  crops  of  fruit.) 
Some  seeds  seem  to  require  a  period  of  rest  before 
awakening.     How    long   is    this    period    in    the    Lima 


44  EXPERIMENTS    WITH   PLANTS 

Bean,  Castor- bean,  Sunflower,  etc?  The  fruit  of  the 
Cockle-bur  contams  two  seeds;  it  is  said  that  one  of 
these  will  germinate  the  first  year  if  given  the  right 
conditions,  but  that  the  other  will  not  germinate 
before  the  second  year. 

How  long  will  seeds  live  if  not  awakened  ?  The 
numerous  accounts  of  seeds,  three  thousand  years  or 
more,  taken  from  mummies  and  made  to  germinate 
are  untrustworthy;  but  there  is  fairly  good  evidence 
that  seeds  which  have  been  deeply  buried  for  many 
years  can  germinate  under  the  proper  conditions. 
It  has  been  found  that  seeds  which  have  apparently 
lost  the  power  of  germinating  can  sometimes  have 
their  vitality  restored   by  soaking  in  certain  ferments. 

A  rapid  method  of  testing  seeds  which  is  often  em- 
ployed is  to  place  them  in  water;  those  which  sink 
are  declared  good,  while  those  which  float  are 
rejected.  Test  some  seeds  in  this  way,  and  plant 
both  those  which  float  and  those  which  sink  (the 
same  number  of  each)  and  record  what  percen- 
tage of  each  germinates.  (This  test  may  work  fairly 
well  for  some  kinds  of  seeds,  but  prove  of  no  value 
in  other  cases.)  Seedsmen  find  it  necessary  to  test 
the  germinating  powers  of  their  seeds  by  accurate 
methods.  For  this  purpose,  the  seeds  are  placed  in 
shallow  trays  on  moist  cloth,  paper,  porous  earthen- 
ware or  plaster  of  Paris  and  kept  at  a  constant  tem- 
perature at  the  degree  which  is  ascertained  by  experi- 


THE    A  WAKENING    OF    THE    SEED  45 

ment  to  be  the  best  for  the  particular  kind  of  seed 
which  is  being  tested. 

What  is  the  best  method  of  keeping  seeds?  Find 
out  what  you  can  about  this  from  gardeners  and  nur- 
serymen. What  special  precautions  are  taken  in  the 
case  of  oily  seeds  ?  Do  you  see  any  reason  why  they 
should  not  keep  as  well  as  starchy  ones  ? 

The  amount  of  water  in  the  seed  affects  its  keeping 
qualities.  If  seeds  are  stored  without  being  sufficiently 
dried,  they  are  very  liable  to  decay.  Ordinarily  they 
are  dried  in  the  sun.  The  pulp  of  soft  fruits  may  be 
removed  by  washing;  this  process  is  hastened  by  add- 
ing a  little  lye  to  the  water  and  allowing  them  to  stand 
for  an  hour  or  so  before  washing.  In  more  difficult 
cases  the  fruits  are  crushed  and  allowed  to  ferment 
before  washing.  If  the  seeds  are  to  be  stored,  they 
should  then  be  carefully  dried. 

Seeds  are  usually  sent  to  or  from  tropical  countries 
sealed  up  air-tight  in  tin  boxes,  to  protect  them  from 
the  moist,  hot  air,  which  causes  them  to  sprout  or  to 
decay.  It  very  often  happens  that  the  seeds  con- 
tain so  much  moisture  that  they  decay  inside  the 
box:  consequently,  both  the  seeds  and  the  pack- 
ing materials  should  be  dried  with  great  care  before 
shipping. 

Ordinarily  seeds  may  be  transported  without  any 
special  precautions.  A  large  part  of  the  flower  seeds 
used  in  this  country  come  from  Germany  each  year 


46  EXPEKIMENTS     WITH    PLANTS 

by  mail  without  any  other  protection  than  a  paper  bag 
enclosed  in  a  cloth  bag  or  wrapping. 

In  general,  a  cool  dry  place  is  best  for  keeping 
seeds.  Some  kinds  of  seeds  should  not  be  thoroughly 
dried.  Hard,  bony  seeds,  such  as  nuts,  seeds  of 
forest  trees,  etc.,  are  most  successfully  preserved  by 
burying  them  in  earth.  A  layer  of  sand  is  placed  on 
the  bottom  of  a  box,  then  a  layer  of  seeds,  another 
of  sand,  and  so  on.  The  boxes  are  then  buried  (one 
or  two  feet  deep)  for  the  winter,  or  they  are  placed 
in  a  shed  and  covered  a  foot  deep  with  straw.  This 
method  closely  imitates  natural  conditions.  Freezing 
is  supposed  to  be  beneficial,  though  not  absolutely 
necessary;  it  probably  helps  to  crack  the  nuts  and  so 
assists  germination. 

What  seeds  germinate  most  quickly  when  favorable 
conditions  come  ?  What  plants  come  up  first  from  seed 
out-of-doors  when  the  season  for  germination  comes  I 
Is  quick  germination  an  advantage  ?  Why  ?  In  making 
a  lawn,  what  usually  comes  up  first, — the  grass  or 
the  weeds  ?  Does  this  help  to  explain  the  success  of 
the  weeds  in  the  struggle  for  light  and  for  space  above 
ground  and  below  ? 

Quick  germination  may  possibly  be  a  disadvantage 
if  the  first  rains  are  succeeded  by  long  periods  of  dry 
weather  so  that  the  seed  which  has  sprouted  dries  out 
again.  Will  the  seed  die  if  allowed  to  dry  up  after 
it   has    sprouted  ?     Allow   some   seeds   to   sprout   until 


THE    AWAKENING     OF    THE    SEED  47 

their  caulicles  are  half  an  inch  long:  then  allow  them 
to  become  thoroughly  dry,  and  again  place  them  in 
a  moist  place.  If  they  sprout  let  them  dry  again ^  and 
repeat  this  as  long  as  they  continue  to  live.  Wheat 
and  Peas  and  Eye  may  be  especially  recommended 
for  this  experiment:  very  favorable  are  also  Oats, 
Buckwheat,  Corn,  Radish  and  Onion. 

Does  light  affect  germination?  Place  two  lots  of 
seeds  on  the  surface  of  the  soil  in  different  pots:  cover 
one  pot  with  a  glass  cover,  the  other  with  an  opaque 
cover  which  extends  to  the  table  so  as  to  exclude  the 
light  completely  (a  pasteboard  cover  is  good  for  this 
purpose).  Place  the  first  pot  in  diffused  light,  the 
second  where  the  seeds  will  be  at  nearly  the  same 
temperature  as  in  the  other  pot.  Thermometers  should 
be  introduced  into  the  pots  so  that  the  temperatures 
may  be  ascertained. 

Some  seeds  (e.  g.,  some  kinds  of  Larkspurs,  Pop- 
pies, etc.)  are  said  to  germinate  imperfectly  or  not  at 
all  in  the  light. 

Will  the  seed  germinate  more  rapidly  if  deprived  of 
its  covers?  Plant  several  kinds  of  seeds,  having  pre- 
viously removed  the  covers  from  half  the  seeds  of 
each  lot.  Plant  some  in  very  moist  earth,  others  in 
earth  that  is  comparatively  dry,  and  take  care  to 
maintain  this  relation  during  the  experiment.  Which 
germinate  first?  In  very  wet  earth  it  often  happens 
that  seeds  deprived  of  their  covers  rot  or  mould,  while 


48  EXPERIMENTS     WITH  PLANTS 

whole  seeds  do  not.  The  rotting  is  perhaps  due  to 
lack  of  air,  and  the  seed-cover  may  prevent  this  by 
keeping  a  certain  amount  of  air  around  the  seed.  The 
cover  likewise  protects  the  germ  from  mould.  But, 
under  favorable  conditions,  and  probably  in  the  great 
majority  of  instances,  the  seed-cover  is  a  hindrance 
to  germination. 

Inasmuch  as  our  experiments  indicate  that  in  very 
many  instances  the  seed-cover  is  a  hindrance  to  germi- 
nation, it  would  seem  to  be  important  for  the  plant  to 
get  rid  of  it  as  soon  as  possible.  This  is  the  next 
problem  to  consider. 

What  covers  seem  hardest  to  burst  open  ?  How  much 
force  does  the  seed  exert  in  bursting  the  covers  ?  We 
may  get  an  approximate  idea  of  this  by  placing  the 
seed  in  a  pair  of  pliers,  as  shown  in  Fig.  38;  one  of 
the  two  handles  of  the  pliers  is  firmly  wedged  in  a 
hole  bored  in  a  block  of  wood,  while  the  other  is 
attached  by  means  of  a  wire  nail,  which  is  bent  as 
shown  in  the  figure  and  passed  through  the  hole  at 
the  end  of  the  rod  attached  to  the  spring  in  an  ordi- 
nary balance.  The  balance  is  to  be  wired  at  the  other 
end  to  a  bolt  which  passes  through  a  hole  in  a  small 
vertical  piece  of  wood  which  is  firmly  screwed  to  the 
block.  On  the  end  of  the  bolt  is  a  nut,  by  turning 
which  the  position  of  the  balance  may  be  adjusted. 
If  a  seed  is  placed  between  the  shorter  arms  of  the 
pliers  and  water  is  poured  into  the  tumbler  until  the 


THE    A  WAKENING    OF    THE    SEED 


49 


seed  is  about  half  submerged,  it  will  soon  begin  to 
swell  and  force  the  free  arm  to  move,  thus  stretching 
the  spring  and  causing  the  indicator  of  the  balance 
to  move  also.  If  a  small  piece  of  glass  be  smeared 
with  vaseline  and  placed  in  front  of  the  indicator, 
it  will  move  forward  with  it  and  record  the  highest 
pressure  reached.  We  may  now  set  the  balance  at 
any  desired  pressure  by  lengthening  or  shortening  one 


38.     Arrangement  for  testing  the  swelling  power  of  a  single  seed. 

of  the  wire  loops,  or  by  turning  the  nut,  or  by  both 
methods,  and  leave  it  for  forty -eight  hours.  If  at 
the  end  of  that  time  an  increase  of  pressure  has  been 
registered,  we  may  replace  the  seed  by  a  similar  one 
of  about  the  same  size,  taking  care  to  set  the  balance 
at  the  outset  at  a  somewhat  smaller  pressure  than  the 
highest  recorded  in  the  experiment  just  finished. 

The  experiment  should  be  watched  and  the  pressure 
recorded  from  time  to  time.    It  must  be  remembered 


50  Exri:inMtjyTs   with  plants 

that  while  the  iorce  with  which  the  seed  swells  may 
be  great,  the  bulk  of  swelling  may  be  small;  hence,  if 
set  at  zero  it  may  raise  the  pressure  only  to  4,  w^iile 
if  it  had  been  set  at  6  it  would  have  raised  it  to  10. 

If  it  w^ere  convenient  to  watch  the  apparatus  con- 
stantly, we  might  get  still  better  results  by  varying 
the  pressure  so  as  to  just  prevent  the  seed  from  swell- 
ing. For  this  purpose  a  short  section  of  ruler  should 
be  attached  to  the  block  near  the  movable  arm  and 
any  motion  of  the  arm  at  once  counterbalanced  by 
turning  the  nut  until  the  arm  returns  to  the  place 
at  which  it  stood  at  the  beginning. 

Owing  to  the  fact  that  the  pliers  act  as  a  double 
lever,  the  pressure  must  be  calculated  as  follows: 
Divide  the  distance  a  b,  from  the  wire  to  the  rivet, 
by  the  distance  c  h,  from  the  (center  of)  the  seed  to 
the  rivet,  and  multiply  by  the  registered  pressure.  In 
order  to  get  the  pressure  per  square  inch,  we  must 
divide  the  calculated  pressure  by  the  area  of  the  seed 
which  is  in  contact  with  one  arm  (if  the  contact  areas 
of  the  two  arms  differ,  an  average  must  be  taken). 

We  shall  probably  find  that  individual  seeds  of 
the  same  kind  var}^  somewhat  in  the  amount  of 
pressure  they  exert;  for  this  reason  it  is  better  to  test 
a  considerable  number  at  once  and  get  an  average 
result.  We  may  do  this  by  means  of  the  apparatus 
shown  in  Fig.  39.  It  consists  of  a  half- pint  agate- 
ware  cup   fitting   into   another   slightly   larger  one   in 


THE 


WAKKXTNG     OF    THE    SEED 


51 


which  the  seeds  are  placed  and  which  has  been  pierced 
with  a  few  holes  to  admit  water:  if  the  bottom  of  the 
onter  cup  is  not  flat,  a  disk  of  wood  should  be  fitted 
beneath  it  so  that  the  pressure  will  not  spring  it.  In 
the  smaller  cup  is  placed  a  block,  on  which  rests  a 
small  iron  support.  For  a  lever  we  use  an  iron  rod 
one  inch  thick  and  three  feet  long,  secured  at  the  end 


39.    Arrangement  for  testing  the  swelling  power  of  a  mass  of  seeds  (a  portion  of  the 
outer  cup  is  represented  as  cut  away  in  order  to  show  the  seeds). 

by  an  eye -bolt,  as  shown  in  the  figui'e.  For  weights 
we  may  use  ordinary  fifteen -pound  iron  hitching- 
blocks,  suspended  from  the  lever  by  hooks.  An 
upright  ruler  near  the  end  of  the  lever  serves  to 
indicate  its  position.  The  whole  apparatus  rests  upon 
a  suitable  board  about  three  feet  long. 

We  commence  the  experiment  by  filling  the  larger 
cup  about  half -full  of  dry  beans  (Pink  Beans  give 
excellent  results)  and  arranging  the  apparatus  as 
shown  in  the  figure   (the  height  of  the  lever  may  be 


52  EXPERIMENTS     WITH   PLANTS 

adjusted  by  means  of  the  nut  at  the  bottom  of  the 
eye- bolt).  Arrange  the  weights  as  desh'ed,  and  pour 
water  into  the  pan  in  which  the  cups  stand.  Observe 
from  time  to  time;  if  the  lever  rises,  move  the  weights 
away  from  the  cups  until  it  sinks  to  the  level  it  occu- 
pied at  the  beginning.  If,  on  the  contrary,  it  falls, 
watch  it,  for  it  will  probably  sink  for  a-  time  and  then 
begin  to  rise,  in  which  case  add  more  weight.  If 
after  forty-eight  hours  no  additional  rise  is  apparent, 
we  may  consider  the  experiment  at  an  end  and  may 
then  proceed  to  calculate  the  pressure  exerted.  This 
we  must  do  for  each  weight  separately.  Thus,  for  the 
first  weight  divide  the  distance  a  chy  a  1)  and  multiply 
by  the  weight;  for  the  second,  divide  a  d  hy  a  b  and 
multiply  by  the  weight.  Add  these  products  together, 
and  then  add  the  pressure  exerted  by  the  bar  itself, 
which  may  be  calculated  as  follows: 

^                       fa  f )  X  (weight  of  bar) 
Pressure  =  ; — r- 

(a  b)  X  2. 

Thus,  if  the  length  of  the  bar  (a  f)  is  thirty- six 
inches,  the  distance  a  h  two  inches  and  the  weight  of 
the  bar  eight  pounds,  the  equation  is 

36  X  8       ^^ 
Pressure  =  -r- — -  =  i2  pounds. 
2x2 

The  results  obtained  by  the  above  methods  are  only 
rough  approximations.  It  should  be  remembered  that 
while,  theoretically,  one  layer  of  seeds  can  exert  as 


THE    A  WAKENING     OF     THE    SEED 


53 


much  pressure  as  several  layers,  nevertheless  we  get  a 
higher  pressure  recorded  when  several  layers  are  used, 
for  the  reason  that  much  of  the  force  which  is  ex- 
pended in  squeezing  the  seeds  together  and  changing 
their  shapes  is  not  recorded,  but  this  error  grows  less 
the  more  seeds  we  use.  Nevertheless,  the  result  must 
always  be  too  small,  for  this  reason. 

That  seeds  exert  considerable  force  in  swelling  may 
be  simply  illustrated  by  means  of  a  fruit -crusher,  as 
shown  in  Fig.  40.  To  calculate  the  pressure,  divide 
a  c  by  a  &,  and  multiply  by  the  pressure  registered  on 


the    spring    balance.     Only 


fraction  of  the  pressure  can  le 
measured  in  this  apparatus.    A 
still  simpler  method 
is    to    fill    a    bottle 


40.  Apparatus  for  dpmon- 
strating  that  swelling 
seeds  exert  pressure  (a 
portion  of  the  vvhII  is 
represented  as  cut  away 
in  order  to  show  the 
seeds). 


54 


EXPElilMENTS     WITH   PLA  NTS 


43. 
Later  stage  of 
germination 
of  SauasVi : 
the  seed- 
leaves  are 
escaping 
from  t  li  e 
seed-cover. 


with  dry  seeds,  put  some  elastic  bands 
about  it  and  place  it  imder  water 
(Fig.  41). 

Do  you  find  any 
devices  to  render  es- 
cape from  the  cover 
easy?   What  seed- 
covers      become 
softer  on  soaking? 
Do    you    find    any 
covers  which   split 
or  break  more  easily 
at  certain   spots, 
thus      permitting 
the  plant  to  escape 
more   readily? 
Examine      care- 
fully seeds  of  the 
Squash,  Walnut, 
Pecan,  Almond, 
and      stones     of 
Peach  and  Plum. 

minates  quickly;  we  may  therefore 
select  it  for  study.  Place  several 
soaked  seeds  flat  on  the  surface  of 
moist  earth,  cover  with  a  piece  of 
glass,  and  observe  them  everj^  day. 
Notice  the  "peg"    (Figs.  42  and  43) 


41.  The  result  of  placing 
seeds  in  a  bottle  under 
water. 

The  Squash  ger- 


THE 


WAKENING     OF    THE    SEED 


50 


I 


which  develops  at  just  the  right  time  and  place  to  do  its 
peculiar  work  of  helping  the  plant  to  get  rid  of  its 
seed -covers.  Could  the  squash  get  out  of  its  covers 
without  the  aid  of  the  ''peg"  ?  Cut  off  the  "peg"  or  slip 
the  cover  up  above  it,  and  see  what  happens.  What 
would  happen  if  the  seed  were  placed  vertically  instead 
of  horizontally?     Try  it  and  see.     The  seeds  should  be 


/, 


w^\^ 


44.     Squash  seeds  jirranged  for  genninalion  experiment. 

firmly  pinned  (at  the  large  end)  to  vertical  strips  of 
wood  (as  shown  in  Fig.  44),  which  are  nailed  to  a 
wooden  block  arid  placed  in  a  pan.  A  little  water 
should  be  poured  into  the  pan  and  a  glass  cover  placed 
on  it  to  prevent  the  moisture  from  escaping.  The 
seeds  should  be  well  soaked  before  being  put  iu  posi- 
tion. Some  may  be  placed  with  the  pointed  end  up, 
others  with  the  pointed  end  down,  and  still  others  with 


56  EXPERIMENTS    }VITn   PLANTS 

the  long  axis  horizontal  but  standing  on  edge  or  lying 
flat  as  shown  in  the  figure.  Remove  the  covers  from 
some  of  the  seeds  before  planting;  does  the  ''peg" 
form  just  the  same? 

What  seed  has  the  hardest  cover?  You  will  prob- 
ably agree  that  it  is  the  Cocoanut.  How  does  the 
plant  get  out  of  it  ?  Where  do  you  find  the  germ  ? 
It  is  very  small  (about  a  third  of  an  inch  long)  and 
lies  under  the  softest  of  the  three  "eyes."  Notice 
how  thin  and  soft  the  substance  of  this  "eye"  is, 
and  you  can  readily  see  that  it  offers  the  plant,  an 
easy  way  of  escape.  Originally  there  ^Yas  a  germ 
under  each  eye,  but  in  the  struggle  for  space  and 
nourishment  two  of  these  germs  have  perished,  leav- 
ing the  survivor  with  a  great  abundance  of  food 
(occasionally  tw^o  of  the  germs  survive).  Almost  any 
wholesale  fruit -dealer  can  procure  for  you  Cocoanuts 
which  have  germinated  during  the  sea  voyage.  These 
are  usually  thrown  away  as  worthless  when  the  cargo 
is  unloaded.  Or  you  can  germinate  them  for  your- 
self by  keeping  them  in  a  hotbed  or  in  a  box  covered 
with  glass  in  the  summer-time.  Plenty  of  moisture 
and  warmth  are  needed  for  success.  They  should  be 
buried  in  earth  or  sawdust  and  kept  where  they  will 
get  as  much  heat  as  possible.  Fig.  45  shows  the 
appearance  of  a  gei'minating  Cocoanut,  with  the  outer 
husk  still  in  position.  This  husk  is  fibrous  and  has 
a  tough  outer  shell,  through  which  the  roots  seem  to 


45.  Germinating  Cocoanut  cut  lengthwise,  showing  the  outer  fibrous  husk,  the  roots 
making  their  way  through  it,  the  young  palm  leaves,  the  meat  enclosed  by  the 
hard  shell  and  the  huge  absorbent  sucker  which,  by  its  growth,  fills  the  cavity 
and  absorbs  both  the  milk  and  the  meat.  At  the  point  of  constriction  between 
the  sucker  and  the  stem  is  the  "eye"  through  which  the  germ  escapes  from  the 
hard  shell. 


58 


EXPERIMEyrS    WITIT    PLAXTS 


penetrate  with  some  ditMculty:  in  many  eases  they  seem 
unable  to  break  through  it,  but  turn  aside  on  reaching 
it  and  grow  down  through  the  fibrous  mass  inside. 
Careful   inspection  of  the  "eye"  where   the  plant   has 

grown  out  through  the  thick 
inner  shell  w^ill  show  how  thin 
the  shell  is  at  this  point  and 
how  very  slight  is  the  ob- 
stacle to  be  overcome  by  the 
plant      in      order     to     break 

46.      Buckeye    cut  open,   showing  the      thrOUgh .  Thc         C  U  O  r  Ul  O  U  S 

r':;:u:.it)''fn/'rpoSt    mucker  developed  by  the  plant 
ipkt)  into  which  the  cauiicie  fits.    f^^.  ^^^Q  purposc  of  absorbiug 

the  food  in  the  Cocoanut  soon  fills  the  whole  cavity 
and  consumes  not  only  the  milk  but  the  fiesh  as  well. 
This  absorbing  organ  is  soft  and  spongy  and  traversed 
by  straight  fibers  (plainly  shown  in  the  figure),  which 
convey  the  mitrinient  directly  to  the  growing  plant. 
Preparations  like  that  shown  in  the  photograph  are 
obtained  by  sawing  the  nut  through  the  middle  (be- 
ginning at  the  larger  end)  to  a  point  about  two  inches 
from  the  "eye,"  and  then  prying  the  halves  apart. 
The  break  then  occurs  exactly  through  the  "eye." 

Do  you  find  that  each  kind  of  seed  has  a  definite 
spot  where  the  first  rupture  of  the  cover  occurs  ?  Is 
this  due  to  the  location  of  the  cauiicie,  to  the  local 
weakness  of  the  cover  ((\  g.,  to  the  presence  of  the 
opening) ,  or  to  mmic  other  cause  ?    WIkmi  th(^  opening 


THE    AWAKENING     OF     THE    SEED 


59 


I.  Buckeye.  The 
plumule  emerg- 
ing from  be- 
rween  the  elon- 
gated stalks  of 
the  seed-leaves. 


ill  the  cover  is  not  near  the  canlicle  (as  in  the  Walnut, 
Peach,  etc.),  where  does  the  rupture  occur? 

What  part  of  the  plant  is  the  first 
to  burst  through  the  opening  ?  What 
advantage  in  this  :  Is  it  the  cauli- 
cle  only  which  grows,  or  do  other 
parts  enlarge  and  help  to  push  it 
out  I  What  part  grows  most  rap- 
idly at  first  in  the  Buckeye?  (See 
Figs.  46  to  49.)  In  the  Walnut? 
In  the  Onion?  What  other  seeds 
are  like  them  in  this  respect !  Do 
the  seed-leaves  grow  at  all  in  such  seeds  as  the 
Scarlet  Runner  ?     What  has   broken  the  covers 

transversely,  as   shown  in 
Fig.  50? 

Does  the  caulicle  invari- 
ably   push    straight   out    through 
the    cover?      Why    does    it 
not  turn    aside  on   meeting 
the  cover,  like  the  roots  of 
the    Cocoanut    in    Fig.  45  ? 
Study   the   germination   of   Corn:    what  is 
the    direction    of    least   resistance    for   the 
caulicle  f       Examine    the     Buckeye,     and 
notice  the   pocket  into  which    the   caulicle 
fits    (Fig.   46,   pli)  :    does    this   direct   its 

48.   Buckeye.    A  \        r>  ?     i-       /  ? 

later  stage.       growtli  ?     Do   you    fiiid    anything    similar 


(id 


b:XPEIiIMENTS     WITH    PLANTS 


in  the  Bean,  Pea  or  other   seeds'? 
(See  Fig.  22.) 

The  surprising  amount  of  force 
developed  by  swelling  seeds   is  ob- 
viously connected  with  the  absorp- 
tion of  water,  by  means   of   which 
they  increase   in  size.      It   is   very 
easy  to  construct  an   apparatus    in 
which  the  absorption  of  water  will 
generate  pressure  just   as 
it  does  in   the   seed.     For 
this    purpose    we    take    a 
piece  of  glass  tubing  about 
one -sixteenth    of     an 
inch  in  diameter  (in- 
side),   or    a   little    larger; 
smooth   one  end  by  heat- 
ing     in     a      flame      until     it  49.    Buckeye,    a  stm  later  stage. 

fuses  slightly,  and  when  it  has  cooled  stretch  over  it  a 
piece  of  ox -bladder  or  heavy  parchment  paper  (ob- 
tainable of  druggists).  Hold  the 
piece  of  bladder  stretched  like  a 
drum -head  across  the  mouth  of 
the  tube,  and  let  an  assistant  wind 
it  tightly  clear  to  the  tube's  mouth 
with    ordinary    cotton   twine;    tie    it 

50.     Scarlet  Runner  Bean      witll    a     SqUarC     kuot    aud     Ict    it    SOak 
germinating;  the  cover      «  ,        -,  •,        -  i,  •    "u 

split  across.  for     several     hours,     during    which 


THE    AWAKENING    OF    THE    SEED 


61 


J 


the  twine  will  shorten  and  make  a  tight  joint.  It  is 
well  to  prepare  several  tubes,  since  some  are  sure  to 
work  better  than  others. 

Place  in  each  tube  a  strong  syrup  (a 
solution  of  sugar  in  water) ,  stand  them  in 
a  tumbler  of  water,  mark  the  height  of  the 
liquid  in  each  tube,  and  leave  them  over 
night.  In  the  morning  it  will  be  found  that 
the  sugar  has  absorbed  water  through  the 
membrane  and  that  the  liquid  has  risen  in 
the  tube.  Choose  the  one  which  shows  the 
greatest  rise,   for  future  experiments. 

To  demonstrate  that  the  absorption  of 
water  can  produce  pressure,  it  suffices  to  fill 
the  tube  completely  full  of  syrup,  invert  in 
a  tumbler  of  syrup  and  tie  on  a  piece  of 
sheet  rubber  (such  as  toy  balloons  are  made 
of) ,  holding  the  end  under  the  syrup  all  the 
time  so  as  to  exclude  air.  The  rubber 
should  be  tied  on  in  the  same  way  as  the 
bladder.  The  tube  may  now  be  rinsed  in 
water  and  then  placed  in  water  as  before 
(see  Fig.  51).  In  a  day  or  so  the  rubber 
will  become  tightly  stretched,  showing  that 
pressure  has  been  generated. 

In  order  to  estimate  how  much  pressure 
is  produced,  we  may  proceed  as  follows: 
Remove  the  rubber  and  fill  the  tube  to  within 


51.  Apparatus 
for  demon- 
strating that 
osmosis  ex- 
erts pres- 
sure. 


62 


UXPhJBfMhWTS     WITH   PLaXTS 


an  inch  and  a  halt'  of  the  top  with  fresh  syrup.  Fit 
a  small  rubber  cork  to  the  tube  and  push  it  down 
about  half  an  inch  into  the  tube;  insert  a 
needle  at  one  side  of  the  cork,  so  as  to  allow^ 
the  compressed  air  to  escape  and  restore  the 
normal  pressure.  Withdraw  the  needle  and 
carefully  dry  out  tlie  inside  of  the  tube 
above  the  cork.  Melt  some  sealing-wax  in 
a  spoon,  and  pour  it  slowly  into  the  tube 
until  it  runs  over.  With  a  hot  knife  smear 
it  over  the  outside  as  far  down  as  the  cork, 
so  as  to  close  the  tube  air-tight  (see  Fig.  52) . 
Obtain  or  prepare  a  strip  of  paper  ruled  in 
fine  divisions  (millimeters  or  twenty -fourths 
of  an  inch,  if  possible),  and  gum  it  to  the 
upper  part  of  the  tube  for  the  purpose  of 
measuring  the  length  of  the  air- column  in 
the  tube.  Place  the  tube  in  water,  note  the 
length  of  the  air -column,  and  observe  it  fre- 
quently during  the  experiment.  The  amount 
of  pressure  produced  in  the  tube  can  be 
easily  calculated  from  the  amount  of  com- 
pression which  the  air  undergoes.  The  for- 
mula for  the  calculation  is : 


52.  Apparat\is 
for  measur- 
ing the  pres- 
sure due  to 
osmosis. 


Lenjjth  of  air-eoluran  at  start  =  Pressure  at  finish, 


Length  of  air-oolnmn  at  finish         Pressure  at  start. 


Thus,  if  the  colunm  measure  one  inch  at 


THE    A  WAKENIXG     OF     THE    SKED  63 

the  start  and  oiio-lialf  inch  at  the  finish  the  equation 
Avill  be 

1  =  Pressure  at  finish. 
%        15  pounds  per  square  inch. 

whence  thirty  pounds  per  square  inch  equals  pressure 
at  finish 

The  results  are  approximate  only  and  will  vary 
according  to  the  charactei*  of  the  membrane,  the 
strength  of  the  syrup,  etc.,  and  cannot  be  regarded 
as  indicating  what  the  same  solution  would  do  with  a 
different  kind  of  membrane  (such  as  is  to  be  found 
in  the  plant,  for  example) ,  but  the  pressure  is  clearly 
demonstrated  and  one  method  of  measuring  it  illus- 
trated. 

In  our  apparatus  the  sugar  attracts^  the  water  with 
considerable  force  so  as  to  generate  the  pressure  we 
have  observed;  we  believe  the  pressure  manifested  by 
swelling  seeds  to  be  generated  in  much  the  same  way, 
by  substances  within  the  seed  (sugar,  proteids,  etc.) 
which  attract  water  with  considerable  force.  We 
have  already  learned  that  if  we  add  water  -  attracting 
substances,  such  as  sugar  or  salt,  to  the  water  in 
which  the  seeds  are  submerged,  these  substances  exert 
a  counter  -  attraction  which  hinders  or  prevents  the 
absorption  of  water  by  substances  within  the  seed. 
We  may  even  withdraw  water  from  the  seed  by  plac- 
ing it  in  a  sufficiently  strong  solution  of  salt  or  sugar. 

'  This  expression  is  used  onlj'  for  the  purpose  of  describing  the  fact  in 
popular  language. 


64  EXPERIMENTS    WITH   PLANTS 

Carefully  weigh  and  measure  a  dry  seed,  place  it 
in  water  for  twenty -four  hours,  and  then  measure  it 
again.  Now  place  it  in  a  very  strong  solution  of  salt 
or  sugar  until  it  returns  to  its  original  weight,  and 
remeasure.  Does  it  return  to  its  original  volume  ? 
After  the  seed  has  grown  for  a  time  it  is  not  possi- 
ble to  shrink  it  back  (by  means  of  strong  solutions 
or  by  drying)  to  its  original  volume,  even  if  we  suc- 
ceed in  bringing  it  back  to  its  original  weight.  The 
growth  has  become  fixed,  or  "set."  The  seed  is  com- 
posed of  very  small  chambers  or  cells  (as  may  be 
easily  seen  by  examining  the  broken  surface  of  a 
Horse-bean  seed-leaf  with  a  hand-lens),  each  of  which, 
like  our  apparatus,  contains  substances  which  absorb 
water  and  so  generate  pressure  by  which  the  walls  of 
the  chamber  are  distended  (just  as  was  the  rubber 
fastened  to  the  end  of  the  tube  in  our  apparatus). 
The  rubber  returns  to  its  original  size  as  soon  as  the 
pressure  ceases.  The  stretched  walls  of  the  cells 
behave  in  the  same  way  at  first,  but  after  a  time  they 
are  strengthened  and  reinforced  by  the  deposit  of 
more  material;  when  this  has  occurred  the  pressure 
may  be  removed  and,  while  they  will  collapse  to  a  cer- 
tain extent,  they  will  not  shrink  back  to  their  original 
size.  The  growth  may  then  be  said  to  be  "set." 
We  may  ascertain  when  this  occurs  by  the  method 
described  above. 

The    explanation    which    has    been    given    of    the 


THE    AWAKENING    OF    THE    SEED 


65 


growth  of  the  seed  applies  to  the  growth  of  all  parts 
of  the  plant  at  all  stages  of  development.  We  may 
cut  off  an  inch  from  the  tip  of  the  root  or  stem  and, 
after  measuring  and  weighing  it,  place  it  in  water, 
where  it  will  continue  to  grow:    we  may  then  deter- 


53.  Section  of  a  bit  of  the  seed-leaf  of  the  Horse-bean,  showing  cells 
filled  with  starch-grains  {st),  the  protoplasm  ipr)  lying  between 
them,  the  nuclei  (/i)  and  the  cell- walls  [cw). 

mine  when  the  growth  has  "set"  by  the  method  which 
we  have  just  used  for  the  seed. 

To  get  a  better  idea  of  the  appearance  of  the  cells, 
we  may  proceed  as  follows :  Holding  a  well  -  soaked 
seed-leaf  of  the  Horse-bean  in  the  left  hand,  cut  thin 
sections  with  a  sharp  razor  held  in  the  right;  cut 
slowly  with  a  drawing  cut,  place  the  sections  in  water 
and  select  the  thinnest  ones,  even  though  they  be 
very  small  pieces.  Place  them  on  a  glass  slide  in  a 
drop  of  water,  cover  with  a  cover- glass  and  examine 
under  the   microscrope.     Fig.    53   shows  the  appear- 


66  JilXPPyh'IM  hWTS     WI  TII   PLA  XTS 

aiiee  of  the  cells  uiuler  the  microscope.  Each  cell 
has  a  cell -wall  {cw)  composed  of  cellulose,  a  firm 
substance  almost  identical  in  nature  with  ordinary 
paper  or  cotton  or  linen  cloth.  Within  this  firm  cell- 
wall  is  the  living  substance  or  protoplasm  (j)r),  soft 
and  jelly-like  in  consistency,  which  can  be  made 
clearly  visible  if  we  place  the  sections  in  weak  eosin 
solution.  It  takes  up  the  eosin  rapidly  and  becomes 
deep  red  in  color,  leaving  unstained  the  cell-wall  and 
the  starch  -  grains  {st)^  which  are  the  white  glistening 
bodies  embedded  in  the  protoplasm.  If  we  place 
some  sections  in  iodine  (see  page  IG-t)  the  starch-grains 
become  bluish  black  and  the  protoplasm  yellow.  If 
we  place  other  sections  in  safranin  solution  until  they 
are  deeply  stained  and  then  rinse  in  alcohol  until  they 
fade  to  a  deep  pink,  we  shall  find  in  each  cell  a  small, 
deeply  stained  body  called  the  nucleus  {n) ;  this  can 
be  more  easily  seen  in  the  outermost  row  of  cells 
(where  there  are  no  starch-grains  to  obscure  it),  and 
still  more  easily  in  sections  of  the  caulicle.  Every 
living  cell  contains  protoplasm  and  a  nucleus,  and  is 
usually  surrounded  by  a  cell-wall. 

The  living  substance  (protoplasm)  of  the  cells  is 
the  source  of  all  their  activities.  It  may  be  killed  in 
a  variety  of  ways;  e.  g.,  by  heat,  poisons,  etc.  It 
then  behaves  very  differently  to  what  it  does  when 
alive.  We  may  kill  some  seeds  to  see  how  this  affects 
their  power  of  growth.     The  most  convenient  way  to 


THE    AWAKENING    OF    THE    SEED 


67 


kill  the  seeds  in  a  dry  condition  is  by  heating  them. 
To  avoid  scorching  them,  we  may  put  them  on  a 
water-bath  consisting  of  two  tin-cups,  as  shown  in  Fig. 
54.  Water  is  placed  in  the  lower  cup,  the  seeds  are 
placed  in  the  upper  one  and  covered,  and  the  appara- 
tus placed  on  a  stove. 
After  the  water  has  boiled 
for  about  an  hour,  the 
seeds  should  be  removed 
and  tested  by  the  methods 
previously  used  for  live 
seeds  (some  should  be 
placed  in  moist  sawdust 
to  see  if  they  are  really 
dead).  How  does  the 
pressure  generated  by 
dead  seeds  compare  with 
that  produced  by  living 
ones  I  To  what  extent  do 
they  "grow"!  Does 
^^  the  growth  become 
"set"? 

We  may,  as  the  result  of  these  experiments,  distin- 
guish two  stages  of  growth,  a  temporary  and  a  perma- 
nent. The  temporary  stage  lasts  until  the  cell -wall 
has  been  sufficiently  reinforced  by  new  material  to 
prevent  it  from  collapsing  when  water  is  withdrawn. 
Cut  off  an  inch  from  the  tip   of   a   root   and   of   a 


54.    Water-bath. 


QS  EXPERIMENTS    WITH  PLANTS 

stem,  kill  it  with  boiling  water,  place  in  water  and 
observe  whether  there  is  any  growth,  i.  e.,  increase 
of  weight  or  length,  and  whether  such  growth  "sets." 

Inasmuch  as  wood  and  many  other  substances 
derived  from  plants  (and  animals)  possess  the  prop- 
erty of  swelling  up  in  water,  even  when  dead,  it  may 
be  interesting  to  compare  them  with  seeds  in  this 
respect.  Test  the  swelling  power  of  dead,  dry  wood 
in  the  same  apparatus  which  you  have  used  for  seeds. 

How  much  w^ater  does  the  wood  absorb  ?  Wood 
has  the  power  of  taking  moisture  from  the  air  to  such 
an  extent  that  it  has  been  used  to  foretell  changes 
in  the  weather  by  means  of  thin  strips,  which  warp 
in  opposite  directions  as  the  air  grows  moister  or 
drier. 

A  very  important  practical  question  is,  whether 
wood  swells  equally  in  all  directions.  Draw  two  lines 
ten  inches  long  on  a  piece  of  dry  plank, — one  with 
the  grain,  the  other  at  right  angles  to  it.  Keep  the 
piece  of  wood  under  water  for  two  or  three  weeks, 
and  then  remeasure.  Find  out  something  about  the 
behavior  of  different  kinds  of  wood  in  shrinking, 
warping,  etc.,  and  the  practical  bearings  of  these  facts. 

These  experiments  will  serve  to  give  clear  ideas 
about  certain  physical  aspects  of  growth  which  are  of 
very  general  application. 


CHAPTER   II 
GETTING   ESTABLISHED 

Do  seeds  germinate  better  on  the  surface  of  the 
ground,  or  when  buried  in  the  soil  ?  Experiment  with 
several  kinds  of  seeds  both  in  the  laboratory  and  out- 
of-doors.  The  amount  of  moisture  in  the  soil  has  a 
great  deal  to  do  with  the  matter  and  should  be  taken 
account  of  in  arranging  the  experiments.  What  seeds, 
if  any,  do  you  find  out-of-doors  germinating  success- 
fully on  the  surface  of  the  soil  ? 

How  do  seeds  get  buried  in  the  soil?  Find  out  all 
you  can  about  the  agencies  which  help  to  bury  seeds, 
including  wind,  rain  and  running  water,  which  cover 
the  seeds  with  earth  and  mud;  cracks  and  fissures  in 
the  earth  into  which  the  seeds  fall ;  burrowing  animals 
and  insects,  such  as  gophers,  ground-squirrels,  wood- 
chucks,  earthworms  and  ants,  which  bury  seeds  acci- 
dentally while  burrowing,  or  carry  them  to  underground 
storehouses;  blue  jays  (and  perhaps  other  birds) ,  wdiich 
are  known  to  store  seeds  by  burying  them  in  the 
ground;  and  various  animals  w^iich  trample  the  seeds 
into  soft  earth  or  mud. 

How  deeply  are  seeds  buried  by  these  agencies  ?  From 

(69) 


70 


EXPEniMFJXTS   wrrn  plants 


a  field  long  fallow,  from  the  margin  of  a  stream  and 
from  the  edge  of  a  wood  take  successive  layers  of 
earth  (each  an  inch  in  depth)  from  the  surface  down 
to  six  or  seven  inches  deep.  Let  these  be  placed  in 
separate  boxes  and  watered,  in  order  to  find  out  how 


5").     Filaree  seeds  hnrvowiiig  into  cotton. 


many  seeds    capable  of   germination  are   contained  in 
each  layer. 

Some  seeds  are  carefully  buried  by  the  parent- 
plants;  the  Peanut  is  one  of  these;  by  all  means, 
watch  this  process  if  possible.  As  the  flower- stalks 
lengthen  they  bend  downward  and  bury  the  Peanuts 
beneath  the  o^round. 


GETTING    ESTABLISHED 


71 


Some  seeds  bury  themselves.  The  Filaree,  Foxtail 
and  Wild  Oats  have  seeds  of  this  kind.  If  you  can 
obtain  these,  place  them  on  the  sur- 
face of  moist  soil  (a  rough,  uneven 
surface  is  best) ,  and  water  them  oc- 
casionally. How  do  the  "clocks" 
assist  in  burying  the  Filaree?  In 
order  to  see  them  work  to  best  ad- 
vantage, they  should  be  placed  (seed 
end  down)  on  moist  cotton  (see 
Fig.  55).  The  seeds  of  the  garden 
Geranium  (or  Pelargonium)  act  in 
the  same  way,  but  to  a  very  slight 
degree  as  compared  with  the  Filaree. 

Buried  seeds, 
which    escape 
from   their  coverings  only  to  find 
themselves  imprisoned   under  ground, 
have  before  them  the  problem  of  get- 
ting their  stems  up  into  the  air  and 
light ;  which  plants  seem  to  achieve  this 
most  easily?    Notice   the  Corn   (Fig. 
56),  which    seems   to   pierce  the  soil 
with  ease  by  means  of  its  sharp  bod- 
kin of  firmly  rolled  leaves;  the  Scar- 
let Runner  (Fig.  57)  seems  clumsy  by 
comparison,     ramming     its     crooked 

,  i?  •!  1  xi  1        J.1  '1  -1  57.     Bean  getting  above 

stem   forcibly   through   the   soil   and  ground. 


56.    Corn  making  its  way- 
above  ground. 


72 


EXPERIMENTS    WITH  PLANTS 


often  lifting  up  a  good -sized  lump  of  earth  on  emerg- 
ing; the  Castor-bean  doubles  and  twists  (Fig.  58),  like 
an  athlete  straining  every  muscle ;  why  does  it  have  so 
much  trouble?  Does  the  growth  of  the  seed-leaves 
while  still  underground  account  for  it  ?  Suppose  we  re- 
move all  hindrances  from  the  Castor-bean;  will  the 
stem  still  form  the  characteristic  "loop"?  Allow  some 
to  germinate  on  the  surface  of  the  soil,  or,  better,  in  a 

flower -saucer  which  has  been 
boiled  (since  Castor -beans  are 
very  apt  to  mould).  Cover 
this  with  a  piece  of  glass  which 
has  been  boiled  in  water  or 
rinsed  in  two  per  cent  forma- 
lin. Remove  the  coats  from 
a  part  of  the  seeds,  so  that 
they  may  be  freed  from  all 
hindrances  which  might  cause 
the  formation  of  the  "loop." 
Place  some  with  the  caulicle 
downward,  others  with  the  caulicle  upward.  Try  the 
same  experiment  with  other  seeds  which  form  a  "loop." 
What  part  of  the  plant  forms  the  "loop"  in  the  Onion  ? 
What  plants  do  not  form  a  "loop"  ?  (Notice  especially 
Corn  and  Grasses.) 

How  much  opposition  can  the  stem  overcome  in  forc- 
ing its  way  upward?  We  may  test  this  by  means  of 
the  apparatus   shown    in    Fig.    59.     Find   two   bottles 


58.  Castor- bean  twist- 
ing itself  into  a  loop 
in  its  efforts  to  pull 
the  seed-leaves  out 
of  the  ground. 


GETTING    ESTABLISHED 


73 


(about  one  inch  in  diameter) ,  one  of  which  fits  inside 
the  other;  cut  off  the  smaller  one  as  shown  in  the 
figure  and  make  a  spiral  spring  of  the  same  diameter. 
(The  spring  is  easily  made  by  winding  a  piece  of 
brass  wire,  about  No.  18,  closely  and  evenly  around  a 
spool.)  In  a  piece  of  board  (which  should  be  about 
an  inch  thick)  bore  a  hole  large  enough  to  snugly  fit 
the  larger  bottle.  Support  this  by  two  blocks  (as 
shown  in  the  figure) ,  so  that  it  may  hold  the  bottle  in  a 
vertical  position.  Allow  the 
plant  to  grow  up  into  the 
smaller  bottle  and  press  up- 
ward against  the  spring:  put 
a  little  cotton-  in  the  bottle 
as  a  cushion  for  the  plant  to 
press  against.  A  suitable 
weight  (about  two  pounds) 
must  be  placed  on  the  ap- 
paratus ;  sufficient  earth 
should  be  removed  at  the 
bottom  of  the  bottle  to  allow 
access  of  air.  Each  day 
mark  on  the  outside  of  the 
larger  bottle  the  height  to 
which  the  inner  bottle  has 
been  raised  (a  strip  of  paper 
gummed  to  the   outer  bottle 

•  n  X?  i.1   •     \  "VT71  ^^-    -Apparatus  for  measuring  the  force 

Will    serve     for    this).        When  of  the  upward  growth  of  the  plaut. 


74 


EXPERIMENTS    WITH  PLANTS 


the  plant  can  compress  the  spring  no  further,  remove 
it,  invert  the  bottles,  substitute  for  the  inner  bottle  a 
larger  one  of  the  same  diameter,  and  pour  shot  into  it 

until  the  spring  is  compres- 
sed to  the  same  point  as  it 
was  by  the  plant.  The  weight 
of  this  bottle  with  the  con- 
tained shot,  plus  the  weight 
of  the  inner  bottle  and  cotton 
(since  the  plant  raised  these 
in  addition  to  compressing 
the  spring) ,  will  give  the  pres- 
sure exerted  by  the  plant:  if 
we  divide  this  by  the  area  of 
the  cross -section  of  the  stem 
just  back  of  the  crook  we 
shall  obtain  the  number  of 
pounds  pressure  to  the  square 
inch.  Thus,  in  one  case  the 
plant  exerted  a  pressure  of 
one  pound.  The  diameter  of 
the  stem  just  back  of  the  crook  was  one -eighth  inch. 
The  equation  is 


Modification  of  tlie  apparatus 
shown  in  Fig.  59. 


1   pound  =1  = 

^R'  3.1416  X  {-h) 


2  81.5  pounds  per  square  inch. 


It  is  interesting  to   note,   in   this   connection,    that 
the  pressure  of   steam  in  the  boilers  of  ordinary  sta- 


GETTING    ESTABLISHED 


75 


61.     An  arrangement  for  weighting  an 
upward-growing  stem. 


tiouary  engines  does  not  usually  exceed  eighty  pounds 
per  square  inch. 

If  a  spring  is  not  at  hand  we  may  use  in  place  of 
it  a  bottle  filled  with  shot,  as  shown  in  Fig.  60. 

A  simple  method  of  test- 
ing the  force  of  the  upward 
growth  of  the  stem  is  by  pre- 
paring a  strainer,  as  shown 
in  Fig.  61,  by  thrusting  the 
finger  upward  through  the 
bottom.  The  plant  is  allowed 
to  grow  up  into  the  cone  thus 
formed  and  receives  both  air 
and  light;  shot  may  be  poured  into  the  strainer  until 
the  plant  can  no  longer  lift  the  weight.  As  it  is  some- 
what difficult  to  bal- 
ance the  load,  we 
may  use  for  this  pur- 
pose the  apparatus 
shown  in  Fig.  6l2. 
Three  stout  wire 
nails,  about  five 
inches  long,  are 
driven  through  holes 
previously  bored  in 
a  board  so  as  to  be 
as  nearly  vertical  as 

•  I  1  rrii  62.    Modification  of  the  arrangement  shown 

possible.      They  are  inFig.ei. 


76  KXPElilMENTS    WITH   PLAJSTS 

SO  placed  that  the  strainer  slips  down  easily  between 
them.  Pieces  of  glass  tubing  about  an  inch  long  are 
attached  by  sealing- w^ax  to  the  sides  of  the  strainer  in 
the  manner  shown  in  the  figure.  (This  is  most  easily 
done  by  attaching  lumps  of  wax  to  the  tubes,  placing 
them  on  the  nails  and  then  heating  the  strainer  at  the 
proper  points.  On  placing  it  in  position  the  wax  will 
adhere  to  it.)  They  should  be  large  enough  to  slip 
easily  over  the  upright  guides.  A  hole  large  enough  to 
receive  a  small  flower -pot  is  now  bored  in  the  board 
and  two  upright  side -pieces  nailed  on  so  as  to  prevent 
the  pot  from  resting  its  weight  on  the  table.  The 
strainer  should  slide  on  the  guides  with  a  minimum 
amount  of  friction. 

It  must  be  remembered  that  if  we  prevent  the  stem 
from  bending  (e.  g.,  by  enclosing  it  in  plaster  of 
Paris),  it  will  probably  exert  a  much  greater  pressure. 
Tne  amount  which  is  registered  by  any  of  these 
methods  is  only  a  very  rough  approximation  and  is, 
as  a  rule,  much  smaller  than  w^iat  the  plant  can  exert. 

We  must  not  be  too  hasty  in  thinking  the  limit  of 
weight  has  been  reached;  for,  after  w^aiting  a  week 
or  so,  the  plant  will  sometimes  begin  to  lift  a  load 
which  seemed  at  first  too  heavy  for  it. 

Plants  sometimes  come  up  through  soil  which  is 
extremely  hard.  It  is  interesting  to  watch  the  be- 
havior of  the  plants  in  a  very  hard,  resistant  soil. 
Observe  all  the  cases  you  can.     Plant  some  Beans 


GETTING    ESTABLISHED 


11 


about  four  inches  deep  and  pack  clayey  soil  firmly 
upon  them.  How  long  before  they  appear  above 
ground  ?  Do  they  come  up  through  the  cracks  (espe- 
cially at  the  sides),  or  not?  Sometimes  they  lift  up 
the  whole  mass  of  earth  as  a  solid  cake  and  thrust 
it  out  of  the  pot.  After  witnessing  a  feat  of  this  sort 
we  are  more  ready  to  believe  the  tales 
about  mushrooms  which  lift  flagstones 
and  the  like. 

In  what  part  of  the  stem  is  the  force 
developed  which  makes  these  feats  pos- 
sible? Bend  a  piece  of  wire  (about  three 
inches  long)  into  a  V,  and  connect  the 
ends  by  a  fine  thread  (a  single  strand 
taken  from  a  silk  thread)  so  that  the  latter 
will  be  stretched  taut;  moisten  this  with 
India  ink  ;  hold  a  cardboard  scale  (or 
ruler)  against  the  stem  and  mark  the  stem 
at  intervals  of  exactly  one- eighth  of  an 
inch  by  touching  it  with  the  inked  thread ; 
stems  devoid  of  hairs  are  most  easily 
marked  (Fig.  63).  The  growth  of  the  stem  will  cause 
the  ink  marks  to  separate,  and  the  degree  of  separation 
will  indicate  the  place  of  most  rapid  growth.  Where 
is  the  region  of  most  rapid  growth?  How  long  does 
the  growth  continue  most  rapid  in  this  particular  re- 
gion ?  How  long  does  this  region  continue  to  lengthen  ? 
How  much  of  the  stem  is  growing  at  a  given  instant  ? 


63.  Bean  with  the 
stem  marked,  in 
order  to  deter- 
mine the  region 
of  greatest 
growth. 


78 


KX  PERI  ME  NTS     WITH   PLANTS 


Stems  and  other  parts  of  plants  may  be  quickly 
and  evenly  marked  by  means  of  the  apparatus  shown 
in  Fig.  64.  It  consists  of  a  small  spool  (such  as  is 
used  for  silk  twist)  with  threads  at  regular  intervals; 
it  revolves  on  a  small  wire  handle.  The  spool  is  first 
notched  at  regular  distances  in  the  following  manner: 
Two  knife-blades  are  fastened  together  (by  clamps  or 
strong  spring  clothes-pins)  with  a  strip  of  wood  (about 
one -twenty -fourth  of  an  inch  thick)  between  them. 
The  double  knife  is  then  pressed  against  the  two 
flanges  of  the  spool,  so  as  to  make  simultaneously 
two  cuts  in  each.     One  blade  is  then  inserted  in  a  cut 

and  the  knife  again  pressed 
down  so  as  to  make  a  fresh 
cut.  By  proceeding  in  this 
way,  all  the  cuts  will  be  the 
same  distance  apart.  A  small 
piece  of  glass  tubing  is  secured 
(by  means  of  sealing-wax)  in 
the  center  of  the  spool,  and 
the  thread  is  firmly  wound 
upon  it  in  a  manner  shown  in 
the  figure.  A  piece  of  wire, 
inserted  in  the  glass  tubing 
and  then  bent  and  twisted  as  shown  in  the  figure,  serves 
as  a  handle.  The  thread  may  be  inked  by  rolling 
the  spool  over  a  pad  (made  by  wrapping  any  absor- 
bent cloth  around  a  stick)  saturated  with  India  ink. 


64.  Contrivauce  for 
marking  stems  in 
the  manner  shown 
in  Fig.  63. 


GETTING    ESTABLISHED 


l^i 


By  means  of  this  apparatus  any  part  of  the  plant, 
even  if  bent  or  crooked,  may  be  instantly  marked 
and  with  much  greater  accuracy  than  if 
done  in  the  usual  way.  In  place  of  a 
spool  we  may  use  two  small  notched 
wheels  (obtainable  of  watchmakers) 
soldered  together  on  a  small  piece  of 
wire. 

What  protects  the  delicate  tip  of  the 
stem  as  it  is  driven  forcibly  through  the 
soil  ?  Compare  the  devices  by  which 
the  Corn  (Fig.  56)  and  Scarlet  Runner 
(Fig.  57)  protect  the  tip.  What  hap- 
pens if  the  tip  is  injured  %  Remove  it 
and  see  (compare  Fig.  65).  Do  new 
branches  arise  ?     When  I     Where  %     In 

65^  Scarlet    Runner     ^l^g^|.   ^^^^^_ 
Bean  with  top  (ter- 
minal bud)  removed.     tloU  do  thcy 

grow  I  Is  this  the  direc- 
tion which  branches  nor- 
mally take  I  What  advan- 
tage in  this  direction  of 
growth  ? 

What  happens  if  a  stem 
meets  an  obstacle  which  it 
cannot  push  aside?     Plant 

some     seeds    two     or     three        ee.     Radish    seedlings    growing    upward 
1-1  .        .       . -1  along  the  glass   side  of  a  box  toward 

mCneS       deep       against      tne  obstacles  placed  in  their  path. 


go  EXPERIMENTS    WITH   PLANTS 

glass  sides  of  a  box,  such  as  is  shown  in  Fig.  QQ.  As 
the  stems  begin  to  grow  up  along  the  glass,  fasten 
small  blocks  of  wood  to  the  glass  (by  means  of  sealing- 
wax)  directly  in  their  paths.  Let  some  of  the  blocks 
have  several  holes  (about  one-fourth  of  an  inch  in 
diameter)  bored  in  them,  to  see  whether  the  plant  wdli 
find  these  and  grow  up  through  them.  Do  you  see  how 
plants  find  the  crevices  in  concrete  and  brick  side- 
walks and  come  up  through  them  I 

Does  the  position  of  the  caulicle  make  any  difference 
in  the  time  it  takes  the   plant  to   get   above  ground? 


67.    Sunflower  seedlings  penetrating  the  soil. 

Plant  (about  an  inch  deep)  an  equal  number  of  seeds 
of  the  same  kind  (at  least  ninety  in  all),. some  with 
the  caulicle  up,  some  with  the  caulicle  down,  some  with 
the  caulicle  at  one  side.  Keep  them  all  under  the 
same  conditions  (as  regards  depth,  moisture,  warmth, 
etc.),  preferably  all  in  the  same  box.  Which  appear 
first  above  ground  ? 

Let  us  see  what  happens  to  the  seed  wdiich  lies 
on  the  surface  of  the  soil.  Its  first  problem  is  to 
get  its  root  down  into  the  ground.  Have  you  ever 
noticed  what  difficulty  some  seeds  have  in  doing  this  ? 


GETTING    ESTABLISHED 


81 


Place  on  the  surface  of  quite  moist  soil  seeds  of 
Mustard,  Morning-glory,  Wheat,  Squash,  Sunflower, 
Onion,  Lima  Bean  and  Horse-bean.  Notice  how  the 
roots  of  the  lighter  seeds,  in  trying  to  penetrate  the 
soil,  raise  the  seeds  up  and  even  turn  them  over,  and 
how  the  root -hairs    and    rootlets    anchor  these   light 


68.     Squash  seedlings  endeavoring  to  penetrate  the  soil. 

seeds  to  the  soil  so  that  the  roots  finally  penetrate  it 
(Fig.  67).  This  is  more  noticeable  when  the  soil  is 
hard  or  firmly  packed  down.  Fig.  68  shows  the 
various  somersaults  performed  by  Squash  seeds  which 
were  all  originally  placed  flat  on  the  surface  of  the  soil. 
How  much  force  can  the  root  exert  in  boring  its 
way  into  the  soil?  The  contrivance  shown  in  Fig. 
69  may  be  used  to  answer  this  question.     It  consists 


82 


EXPKinMKyrs   with  plants 


of  a  stndent-laiup  chimney  (sizo  No.  1) 
containing  several  corks  (small  enough 
to  slide  easily  in  the  chimney)  fastened 
together  end  to  end  by  means  of  sealing- 
wax.  In  the  enlarged  base  of  the  chim- 
ney a  large  cork  or  wooden  disk  is  fitted, 
through  which  passes  a  clothes-pin  of 
the  sort  indicated  in  the  figure.  Through 
the  wire  coil  in  the  clothes-pin  passes  a 
wire  nail,  which  is  firmly  held  in  place  by 
two  wire  loops,  which  are  securely  fast- 
ened to  the  narrow  neck  of  the  chimney; 
another  wire  is  passed  around  the  chim- 
ney just  below  the  nail,  to  hold  the  wire 
loops  in  position.  A  stopper  is  inserted 
in  the  end  of  the  chimney  and  water 
poured  in.  A  Horse-bean  with  a  caulicle 
about  a  quarter  of  an  inch  long  is  inserted 
in  the  clothes-pin,  which  is  then  firmly 
wedged  into  the  cork  (a  small  wooden 
wedge  may  be  used  if  necessary),  and 
placed  in  such  a  position  that  the  tip  of 
the  caulicle  rests  in  a  small  excavation  in 
the  center  of  the  topmost  cork.  If  the 
pressure  of  the  cork  float  is  so  great  as  to 
break  or  injure  the  root,  stick  a  pin  into 
the  topmost  cork  in  such  a  way  as  to 
temporarily  remove  the  pressure  from  the 


i9.  Apparatus  for 
determining  how 
much  t'orf'e  tlie 
root  exerts  in 
growing  down- 
ward. The  rnoT 
denre.sses  the 
cork  float. 


I 


GETTING    ESTABLISHED  83 

caulicle;  the  caulicle  will  soon  gi'ow  down  and  press 
against  the  cork.  The  amount  of  pressure  may  be  reg- 
ulated by  the  amount  of  water  placed  in  the  chimney. 
The  wire  nail  is  now  passed  through  the  two  wire  loops 
and  the  coil  of  wire  in  the  clothes-pin.  The  clothes- 
pin is  now  firmly  held  at  two  points,  and  may  be 
wedged  if  necessary.  The  seed  should  be  surrounded 
by  moist  cotton,  and  grooves  should  be  cut  in  the 
edge  of  the  cork  to  admit  air. 

On  a  strip  of  paper  gummed  to  the  outside  of  the 
chimney  marks  should  be  made  from  time  to  time 
to  indicate  the  position  of  the  float.  When  the  plant 
can  depress  it  no  farther,  the  force  exerted  should  be 
measured  by  removing  the  clothes-pin,  etc.,  and 
depressing  the  float  (by  means  of  a  bottle  filled  with 
shot)  to  the  lowest  mark  recorded  on  the  gummed 
slip.  The  pressure  per  square  inch  may  then  be 
calculated,  as  in  the  case  of  the  stem,  by  finding  the 
diameter  of  the  root  just  back  of  the  tip. 

Another  simple  appai'atus  may  be  arranged  to  test 
the  pressure  of  the  root,  as  shown  in  Fig.  70.  It  con- 
sists of  a  tube  filled  with  earth,  into  which  the  root  is 
allowed  to  grow,  and  a  larger  tube  into  which  this  fits ; 
the  larger  tube  contains  a  wire  spring,  which  is  com- 
pressed by  the  growth  of  the  root.  The  larger  tube 
may  be  one -fourth  of  an  inch  in  diameter:  the 
smaller  tube  should  slide  easily  inside  it;  its  edges 
should  be  smoothed  in  a  flame.      It  is  well   to  break 


84 


EXPERIMENTS    WITH  PLANTS 


off  the  pointed  end  a  little  so  as  to  allow  a  small  open- 
ing for  drainage;  to  prevent  the  root  from  growing 
through  this  opening,  close  it  wdth  a  piece  of  gravel. 
The  spring  should  be  of  such  a  stiffness  that  an  ounce 
will   compress   it    about  an   inch.      Such   a   spring   is 

easily  made  by  winding  a  brass 
wire  closely  and  evenly  on  a 
round  stick  (about  one-eighth 
of  an  inch  in  diameter) .  Se- 
cure the  tubes  with  wire  (or 
elastic  bands)  to  a  strip  of 
wood,  as  shown  in  the  figure; 
pin  the  seed  to  this  strip  and 
clamp  a  small  piece  of  wood 
above  for  it  to  press  against; 
the  clothes-pin  which  secures 
the  piece  of  wood  also 
serves  to  secure  the 
whole  apparatus  to  a 
tumbler  filled  with 
water.  Arrange  a  strip 
of  cotton,  as  shown  in 
the  figure,  to  keep  the  seed  moist;  take  care,  however, 
that  the  soil  in  wiiich  the  root  grows  is  not  kept  too 
moist,  since  in  that  case  it  will  probably  rot.  As  the 
root  grows  it  forces  the  tube  downward,  compressing 
the  spring;  when  it  comes  to  a  standstill,  remove  the 
root  (but  not  the  earth)  from  the  inner  tube  and  place 


70.    Apparatus  for  determining  the  force  of 
growth  of  a  root  by  means  of  a  spring. 


GETTING    ESTABLISHED  85 

Upon  the  latter  a  funnel  closed  at  the  bottom  with 
a  stopper;  into  this  pour  shot  until  the  spring  is  com- 
pressed to  the  same  point  as  it  was  at  the  end  of  the 
experiment.  The  weight  of  the  funnel  with  the  con- 
tained shot  gives  the  pressure  exerted  by  the  root. 

By  preventing  the  root  from  bending,  as  suggested 
on  page  76,  we  could  obtain  much  larger  pressures. 
Such  a  condition  of  things  would  occur  naturally  only 
in  a  very  firm  soil. 

Another  way  to  roughly  test  the  power  of  the  root 
to  penetrate  the  soil  is  to  use  a  box  with  a  bottom  of 
wire  netting  (the  meshes  being  about  five-eighths  of  an 
inch  square) .  On  the  netting  place  cloths  of  various 
thicknesses,  tin-foil,  slices  of  potato,  or  anything  else 
that  the  class  may  suggest.  Fill  the  box  with  earth 
and  plant  the  seeds ;  it  may  be  easily  observed  if  the 
roots  are  able  to  penetrate  any  of  these 
objects;  for  this  purpose  hang  the  box 
at  a  convenient  height. 

What  part  of  the  root   develops   the 
energy  necessary  for  such  strong  growth  ? 
Eemove  some  roots  which  are  growing 
in   moist    air    (as   shown   in   Fig.    78). 
Mark  them  in  the  same  way  as  you  have    71.  Root  marked  in 
already   marked    the    stem    (Fig.    71).       theTeii'onof^^ea"^ 
Remove  only  one  root  at  a  time,  mark      *^*  e^owth. 
it  and  place  it  as  quickly  as  possible  in  water,  where 
it  will  continue  to  grow.     Strong  roots,  such  as  those 


86  j!]XPEIiIMEXTS     WITH    PLANTS 

of  the  Horse-bean,  Lima  Bean,  Buckeye,  or  the  roots 
of  an  Onion  bulb  are  best  for  this  experiment.  In 
what  region  is  the  most  rapid  growth  ?  How  long 
does  it  continue  in  this  particular  place!  To  what 
region  does  it  then  move? 

When  the  root  forces  its  way  into  the  soil  so  ener- 
getically, what  protects  the  delicate  tip  from  injury? 
Notice  the  protective  cap  which  covers  the  end  of  the 
root.  Roots  of  Wandering  Jew  grown  in  water  (Fig. 
85),  caulicles  of  Sunflower,  Squash,  etc.,  show  this 
cap  well.  Can  you  find  it  in  other  plants  ?  Use  a  lens 
if  necessary.  Why  is  the  tip  the  most  tender  and 
delicate  part  of  the  root  ?  Why  can  it  not  be  strength- 
ened by  tough  woody  fiber  ?  Would  such  fiber  prevent 
growth?  Would  it  be  an  advantage  to  locate  the 
growing  region  elsewhere  than  at  the  tip  ?  What 
would  happen  to  the  side  roots  and  root-hairs  (which 
are  firmly  fastened  in  the  soil)  if  the  growing  region 
were  above,  instead  of  below,  them  ? 

What  happens  if  the  tip  is  injured?  Remove  the 
tips  from  tap-roots  growing  in  water;  do  new  roots 
appear  ?  Where  do  they  arise  ?  In  what  direction  do 
they  grow  I  What  advantage  in  this  peculiar  direction 
of  growth  ! 


CHAPTER    III 


THE  WORK  OF   ROOTS 


What  is  the  function  of  the  root?  Find  six  healthy 
plants  of  about  the  same  height.  By  an  oblique  cut 
sever  the  main  roots  of  three  of  these  about  half  an 
inch  below  ground,  disturbing  the  earth  as  little  as 
possible.  It  will  be  necessary  to  support  the  plants 
by  tying  them  to  a  stick  thrust  into  the  soil  (Fig.  72). 
This  calls  attention  to  one  important  function  of  the 
root,  namely,  to  anchor  the  plant  in  the 
soil\  What  sort  of  root  is  best  adapted 
to  anchor  the  plant  firmly,  a  straight, 
deep  root  or  a  shallow,  spreading  one  ? 
What  plants  are  hardest  to  pull  up  !  Ex- 
plain why  this  is  so.  What  kinds  of 
trees  are  most  easily  uprooted ;   wh}^  ? 

Examine  the  injured  plants  every  day 
and  note  any  abnormal  symptoms.    Notice 

1  The  roots  of  Carrot,  Bulbous  Buttercup  and  many 
other  plants  (especially  such  as  grow  in  crevices  of  rocks, 
or  such  as  hug  the  ground)  contract  when  full  grown  and 
pull  the  plant  down  some  distan?e  into  the  soil.  The  tips 
'of  many  Blackberry  vines,  which  take  root  in  contact  with 
the  soil,  are  soon  drawn  beneath  the  surface  by  the  con- 
traction of  the  roots.  iMake  observatiojis  on  this  point. 
What  advantage  in  this  action  of  the  root  ? 


2.  Plant  attached 
to  support  ready 
to  liave  tlie  root 
cut  off. 


(87) 


88 


EXPERIMENTS    WITH  PLANTS 


any  changes  in  the  color,  shape  or  position  of  leaves 
and  other  parts.  What  do  you  think  these  indicate  ? 
Allow  some  uninjured  plants  to  go  un watered  for  a 
time ;  do  they  show  the  same  symptoms  ?  What  does 
this  indicate  as  to  the  work  of  the  root  ? 

In  what  direction  should  the  main  root  grow,  to  do 
its  work  most  effectively?  Does  the  main  root  always 
grow  straight  down?  Pin  soaked  seeds  on  corks  in 
various  positions  (see  Fig.  73),  and  allow  the  corks 
to  float  on  water;  pin  the  seeds  in  such  a  position  that 
they  will  remain  partly  submerged;  cover  the  dish 
with  a  piece  of  glass.  Put  some  soaked  seeds  in 
various  positions  on  the  surface  of  moist  soil  and 
cover  with  an  inverted  tumbler,  or  place  them  in  a  pot 
half  full  of  soil  and  lay  a  piece  of  glass  on  the  top, 

to  keep  the  air  moist. 
If  the  roots  bend 
downward,  change 
the  position  of  the 
seeds  so  that  they 
point  upward  or  lie 
horizontally.  Do  they 
begin  to  grow  down- 


73.     Seeds  pinned  to  corks  -which  are  floating 
on  water. 


ward  again  ? 


Why  does  the  main  root  persist  in  doing  this,  no 
matter  in  what  position  it  is  placed?  The  idea  has 
been  advanced  that  the  tip  of  the  root,  being  not  very 
rigid,  droops   downward  of  its  own  weight  and  that 


THE    WORK   OF  ROOTS  89 

this  starts  the  growth  in  the  right  direction.  This 
idea  may  be  tested  by  a  very  simple  experiment.  In 
a  small  saucer,  place  some  mercury;  fasten  two  or 
three  clothes-pins  to  the  side  of  the  dish  (Fig.  74) ;  to 
these  pin  germinating 
seeds  (Peas  are  especially 
good)  with  perfectly 
straight  caulicles  about 
half  an  inch  long;  let  the 
caulicles,  especially  at  the 

-  -  _       74.     Seeds   arranged   with    their  caulicles 

tip,    rest    on   tne    SUriaCe    OI  resting  on  mercury,  •which   is   covered 

the  mercury.  Pour  in  with  a  mtie  water. 
enough  water  to  partially  submerge  the  seed.  If,  now, 
the  root -tip  bends  downward  into  the  mercury,  over- 
coming its  resistance,  the  idea  that  it  droops  of  its  own 
weight  cannot  be  correct.  If  the  mercury  is  not  clean 
it  may  kill  the  root,  since  mercury  salts  are  poisonous ; 
it  is  well,  therefore,  to  first  clean  the  mercury  with  a 
little  cotton  wool,  and  afterwards  with  running  water. 
In  place  of  mercury  we  may  use  gelatine  (one  part  of 
gelatine  dissolved  in  five  of  water),  in  which  case  no 
water  is  to  be  placed  in  the  dish,  but  it  should  be 
covered  with  a  piece  of  glass  to  prevent  the  roots  from 
drying  up. 

What  starts  the  root  in  the  right  direction?  Is  it 
light,  moisture,  air,  warmth,  food  or  gravity  ?  We 
may  test  the  first  five  simultaneously  by  a  very  simple 
experiment.      Fill    a    box  (having    a    bottom  of   wire 


90  EXPERIMENTS    WITH    PLANTS 

netting)  to  one-half  its  depth  with  damp  sawdust;  on 
this  lay  the  seeds,  well  soaked,  and  add  enough  saw- 
dust (equally  damp  with  the  first)  to  fill  the  box  even 
with  the  top.  On  top  of  this  put  several  layers  of 
well-soaked  cloth  or  blotting  paper,  and  keep  this  wet 
during  the  experiment;  let  the  edges  press  closely 
against  the  box.  Hang  the  box  up  so  that  the  under 
side  may  be  easily  observed.  Air,  light  and  warmth 
now  come  mostly  from  below  instead  of  mostly  from 
above,  while  moisture,  ordinarily  more  abundant  be- 
low the  seed,  is  now  about  equally  abundant  above 
and  below,  and  the  same  is  true  of  any  food  the 
moisture  contains.  Since  the  sawdust  is  alike  in  depth 
above  and  below,  it  cannot  influence  the  roots  to 
rn-ow  in  one  direction  more  than  in  another. 

If,  now,  the  roots  grow  downward  (and  the  stems 
upward)  it  must  be  in  obedience  to  some  influence 
other  than  these. 

Perhaps  this  is  gravity :  How  can  we  test  this  sug- 
gestion? What  would  happen  if  we  should  make  the 
force  of  gravity  of  no  effect  by  placing  the  seeds  on  a 
revolving  w^heel?  If  the  wheel  turns  always  at  the 
same  rate,  each  side  of  the  root  will  in  its  turn  be 
underneath  for  a  short  time,  but  no  side  more  than 
another.  So  when  all  sides  are  equally  affected  by 
the  downward  pull  of  gravity,  will  it  influence  the  root 
to  grow  in  any  one  direction  more  than  in  another  ? 
We  may  use  the  apparatus  shown  in  Fig.  75  to  answer 


THE     WOBK    OF   BOOTS 


91 


this  question.  The  essential  parts  are  an  ordinary 
clock  and  a  small  tub  (of  wood  or,  better,  of  wood 
fiber) ,  with  two  holes  to  admit  a  stiff  wire  or  knitting- 
needle.  The  wire  should  be  bent  at  one  end  and 
wired  to  the  minute-hand  of  the  clock.  In  order  to 
prevent  the  minute-hand  from  slipping,  it  may  be 
necessary  to  fasten  it  to  its  axle  with  a  little  solder  or 


Arrangement  for  causing  germinating  seeds  to  revolve  slowly. 


sealing-wax.  Short  bits  of  glass  tubing  are  inserted 
in  the  holes  in  the  tub,  to  act  as  bearings.  The  ger- 
minating seeds  are  to  be  pinned  to  corks  impaled  on 
the  wire;  the  roots  should  point  in  various  differ- 
ent directions;  pour  sufficient  water  into  the  tub  so 
that  the  seeds  dip  in  it  each  time  they  revolve;  cover 
the  tub  with  a  piece  of  glass,  place  over  this  a  piece 


of  cardboard  or  cloth   to   exclude 


ight. 


and   set  the 


92  EXPERIMENTS    WIIH   PLANTS 

clock  going.  The  roots  grow  well  under  these  con- 
ditions; do  they  continue  to  grow  in  different  direc- 
tions, or  do  all  assume  the  same  direction?^  Does  this 
(in  connection  with  the  previous  experiments)  indicate 
that  it  is  gravity  which  causes  all  roots,  under  ordi- 
nary circumstances,  to  assume  the  same  direction? 
How  do  the  stems  behave  ?  It  seems  at  first  rather 
puzzling  to  conclude  that  gravity,  which  causes  roots 
to  grow  downward,  also  causes  stems  to  grow  upward; 
but  there  seems  to  be  no  escape  from  such  a  conclusion. 
We  may  now  go  a  step  further  and  substitute  an- 
other force  for  that  of  gravity.  This  we  may  do  by 
making  the  wheel  revolve  more  rapidly.  If  a  piece 
of  wire  is  bent  around  the  spoke  of  a  wheel,  so  as  to 
form  a  loose  ring,  and  one  spins  the  wheel,  the  ring 
will  be  hurled  to  the  rim  by  a  force  commonly  called 
centrifugal  force.  If  the  wheel  be  turned  rapidly 
enough,  the  centrifugal  force  will  be  much  greater  than 
the  force  of  gravity.  Will  a  seed  ]'evolving  rapidly 
on  such  a  wheel  direct  its  roots  in  accordance  with 
the  centrifugal  force?  To  test  this,  we  may  construct 
a  water-wheel  as  shown  in  Fig.  76.  Cut  out  of  thin 
sheet  zinc  a  circular  piece  six  inches  in  diameter. 
Have  this  cut  to  allow  the  insertion  of  corks,  as  shown 

1  It  may  happen  that  the  root  will  grow  on  perfectly  straight  in  the  direc- 
tion given  to  it  when  fastened  to  the  cork,  or  it  may  bend  as  the  result  of  in- 
jury, influence  of  moiiture,  light,  etc.  If  such  bendings  do  not  occur  in  the 
control  experiment  (which  should  be  made)  it  indicates  that  the  directive  force 
■which  prevents  such  bendings,  and  causes  all  the  roots  to  grow  in  the  same 
direction  in  the  control  experiment,  has  been  nullified  by  the  revolving  wheel 


THE    WORK    OF   BOOTS 


93 


in  the  figure.  Let  the  flaps  made  by  cutting  remain  in 
place.  Fix  round,  flat  corks  in  the  cut  places,  and 
bend  the  flaps  so  as  to  support  the  corks  as  firmly 
as  possible.  For  the 
axle  use  a  knitting 
needle,  impaling  two 
rubber  stoppers 
upon  it,  one  on  each 
side  of  the  zinc  disk, 
to  hold  the  latter  in 
place.  They  should 
press  firmly  against 
the  disk,  to  insure 
its  turning  with  the 
axle.  The  two  up- 
right wooden  sup- 
ports fastened  to  a 
block  of  wood  are 
pierced  by  holes  just  large  enough  to  admit  the  small 
glass  tubes  in  which  the  axle  rests.  Each  of  these  is 
closed  at  the  end,  to  keep  the  axle  from  slipping  too 
far.  We  place  the  apparatus  in  a  sink,  and  attach  a 
rubber  tube  to  a  faucet.  At  the  end  of  this  tube  is  a 
piece  of  glass  tubing  drawn  to  a  point.  The  manner 
in  which  this  is  supported  is  shown  in  the  figure.  It 
should  be  wedged  firmly  in  place  by  wooden  wedges, 
and  be  so  directed  that  the  stream  will  strike  the 
wheel  just  at  its  rim.     The  stream  must  be  powerful 


Water-wheel  for  the  purpose  of  making 
germinating  seeds  revolve  rapidly. 


94  EXPEBIMEXTS    WJTff    PLANTS 

enough  to  make  the  wheel  revolve  rapidly  (two  or 
three  times  a  second).  A  piece  of  cloth  must  be  put 
over  and  around  it,  like  a  tent,  to  confine  the  flying 
drops.  Germinating  seeds  (preferably  Peas)  should 
be  pinned  to  the  corks  on  the  sides  not  struck  by  the 
stream  of  water.  In  the  course  of  a  day  or  so,  pro- 
vided the  wheel  is  turning  rapidly  enough,  we  shall 
expect  to  see  the  roots  all  bending  away  from  the  cen- 
ter of  the  wheel  and  growing  straight  out  in  the  direc- 
tion of  the  radius,  while,  on  the  other  hand,  the  stems 
grow  straight  in,  pointing  toward  the  center  of  the 
wheel. 

Let  us  see  what  will  happen  if  we  place  the  ap- 
paratus on  its  side  so  that  the  wheel  revolves  horizon- 
tally. If  the  plants  have  become  inconveniently  large 
we  may  replace  them  by  fresh  ones  with  caulicles 
about  an  inch  long.  Two  forces  now  act  on  the  plants, 
— the  centrifugal  force  and  that  of  gravity.  The  roots 
take  up  an  intermediate  position,  growing  away  from 
the  center  of  the  wheel  as  before,  but  also  obliquely 
downward;  the  stems  grow  in  the  opposite  direction. 

These  experiments  lead  us  to  think  that  when  root 
and  stem  issue  from  the  seed,  gravity  determines  the 
direction  in  which  they  grow:  we  can  therefore  under- 
stand how  the  seed,  whether  above  ground  or  below, 
unerringly  sends  its  stem  and  root  in  the  right  direc- 
tion. We  can  readily  see  that  this  is  an  important 
matter  for  the  plant,  for  the  quicker  it  gets  its  stem 


TJIJ^J    WOBK    OF   BOOTS 


95 


above  ground  into  the  light  and  air  and  its  root  down 
into  the  soil  the  better  will  be  its  chances  of  living 
through  this  period  of  its  life,  which  is  more  critical 
and  more  beset  with  dangers  than  any  other.  We  can 
also  see  that  in  this  connection  gravity  is  the  best  guide 
the  plant  could  have,  since  it  is  more  constant  and 
uniform  than  any  other  —  the  only  one,  in  fact,  that  is 
absolutely  constant. 

What  happens  if  the  root  in  its  downward  course 
meets  with  a  dry  region?  When  seeds  are  grown  in 
damp  sawdust,  in  a  box  provided  with  a  bottom  of  wire 
netting,  as  described  on  page  90,  how  do  the  roots  be- 
have as  they  grow  down  through  the  netting  into  the 
dry  air  I  Often  we  see  them  turn  upward,  as  in  Fig. 
77.  Is  this  be- 
cause they  try  to 
avoid  air,  light, 
etc.,  or  are  they 
attracted  by 
something  in  the 
sawdust?  We 
may  test  this  by 
arranging  the  ex- 
periment as  fol- 
lows: Fill  a  tumbler  one-third  full  of  water  and  tie  a 
piece  of  cheese-cloth  over  the  top;  on  this  put  damp 
sawdust,  and  in  the  sawdust  place  several  soaked  seeds ; 
invert  another   tumbler  over  the  whole,  as    shown  in 


77.    Arrangement  for  testing  the  effect  of  moisture  on 
the  direction  of  growth  of  roots. 


96 


EXPERIMENTS    WITH  PLANTS 


Fig.  78.    Do  the  roots,  on  emerging  from  the  sawdust, 

turn  back  to    it?      The  air  now   contains  much  more 

moisture  than  before,  but  in  other 

respects     there     is     no     essential 

change.      It   would   seem  that  in 

the  first  instance  they  turned  back 

because  the  air  was  so  dry,  or,  in 

other  words,  were  attracted  by  the 

water  in  the  sawdust. 

As  a  matter  of  fact,  we  know 

that  tree  roots   find   (and  fill  up 

more  or  less  completely)  cisterns 

and   drains  which  are  three  hun- 
dred feet  or  more  distant  from  the 

tree;    in   many  towns  there   exist 

ordinances   prohibiting  the  main- 
tenance of  certain  trees  within  a 

hundred  feet  of  a  sewer. 

In  the  above  experiments  the  roots  are  not  under 

perfectly  natural   conditions;    we  may  approach  these 

more  nearly  by  the  ar- 
rangement shown  in  Fig. 
79.  In  the  middle  of  a 
box  of  earth  place  a 
flower- pot,  the  hole  of 
_  .  •       T,  .1,       which    has    been    tightly 

79.    Arrangement  for  ascertaining  whether  *="         •^ 

rL';;:,\l"ls«f.l7wl;":atr.wMeh     dosed    by   a    rubber    or 
?Ku.''S«otiTew.r  ""'"  ""°     cork  stopper  or  by  seal- 


78.  Arrangement  to  test  the 
behavior  of  roots  in  moist 
air.     (Sectional  view). 


^^--^^^^-^ 

'f4:-: 

1 

TEE    WORK   OF  BOOTS 


97 


ing-wax.  Let  the  earth  be  reasonably  moist  when  the 
seeds  (well  soaked)  are  placed  m  it,  but  do  not  water 
it  further  except  by  pouring  water  into  the  flower-pot, 
from  which  it  will  diffuse  through  the  soil.  After  a  few 
days  examine  the  roots,  to  see  what  direction  they 
have  taken.  What  is  the  greatest  distance  from  the 
flower-pot  at  which  the  direction  of  growth  of  the  roots 
is  aifectedf  By  using  a  shallow  box  (about  one  and 
one-half  inches  deep),  with  a  glass  bottom,  and  plac- 
ing the  earth  directly  on  the  glass,  we  can  watch  the 
growth  of  the  roots  without  disturbing  them;  but, 
since  the  glass  affords  no  drainage,  very  little  water 
may  be  used ,  else  the  soil  will  become  so  saturated 
with  moisture  as  to  spoil 
the  experiment.  The  re- 
sult will  depend  partly 
on  the  amount  of  water 
present  and  partly  on 
whether  the  roots  are 
growing  in  sand,  clay  or 
sawdust. 

What  direction  should 
the  side  roots  take  to 
explore  the  soil  most 
effectively  for  moisture  ? 
glass    side     (see 


80.    Apparatus  for  observing  the  behavior 
of  roots  as  they  encounter  obstacles. 


In  a  box  with  a  sloping 
Fig.  80),  filled  with  moist  soil, 
place  several  seeds  with  caulicles  (about  an  inch 
long)   pointing    straight    downwards.      Mark    on    the 


98 


EX  PERT  ME  NTS    M'TTH    PLANTS 


glass '-■  the  direction  which  seems  to  you  most   advan- 
tageous  for    the   main  roots   and    side   roots   and  the 

rootlets  which 
spring  from  the 
latter  ;  begin  the 
marking  directly 
over  one  (or  more) 
of  the  roots.  Ex- 
clude light  com- 
pletely by  covering 
the  glass  with  card- 
board or  cloth. 

What  direction  do 
the  side  roots  have 
when  they  burst 
out  of  the  main 
root?  Do  they  after- 
ward change  this 
M       .    A  ■     , .  .  .  .X.  V.  u   ■     ,  -A      direction  ?     I  f   s  o , 

Apparatus  designed  to  test  the  Dehavior  of  side  ' 

roots  under  the  influence  of  gravitj'.  -^  hen?        Do      VOU 

think  they  solve  the  problem  of  direction  in  the  best 
way? 

Are  they  guided  in  the  direction  they  take  by  light, 
heat,  moisture,  food  or  gravity?  Light  has  been  care- 
fully excluded.  If  it  were  heat,  moisture  or  food  that 
guided  them,  we  should  expect   to  find  adjacent   side 

1  A  mixture  of  glue  and  whiting  put  on  with  a  brush  is  excellent  for  mark- 
ing;  white  paint  will  do,  but  dries  more  slowly;  yellow  pencils  for  marking 
glass  are  good. 


THE     WOliK    OF   BOOTS 


99 


roots  turning  in  the  same  direction,  instead  of  which 
they  radiate  in  all  directions  from  the  main  root;  and 
not  only  so,  but  roots  from  neighboring  plants  cross 
each  other  growing  in  opposite  directions.  Is  it, 
then,  gravity  ?  We  may  test  this  very  simply. 
When  the  side  roots  have  grown  some  distance,  tip  up 
the  box,  as  in  Fig.  81.  Carefully  mark  on  the  glass 
the  position  of  each  side  root;  mark  with  especial  care 
the  position  of  the  tips.  Leave  the  box  undisturbed 
and  make  daily  observations. 
Do  the  side  roots  change 
their  direction  I  Do  the 
rootlets  which  spring  from 
them  change  theirs  ? 

As  we  watch  the  roots 
growing  along  inside  the 
glass,  we  may  occasionally 
see  them  encounter  small 
sticks  or  stones  or  other  ob- 
stacles; what  do  they  do 
then?  Obstacles  may  be  pro- 
vided in  abundance  by 
fastening  small  pebbles  or 
blocks  of  wood  to  the  glass 
with  sealing-wax  before  put- 
ting the  soil  in  the  box  (Fig. 
80) ,  or  to  the  sides  of  a  glass 
funnel  (as  in  Fig.  82).     Do     '''  -^^-^f •-'-'.' "^/^---^p^-atus 

c5  y  .         j_^w  shown  in  Fig.  SO. 


100 


EXPERIMENTS    WITH  PLANTS 


the  roots  diverge  from  their  course  more  than  is  ab- 
solutely necessary  to  avoid  the  obstacles?  Do  they 
resume  their  original  course  as  soon  as  they  have 
passed  the  obstacles  ? 

Study,  as  far  as  is   practicable,  the  rootlets  which 
spring  from  the  side  roots  in  the  same  way  in  which 


-   ^v  >  !>    . 


^^me- ' 


'*'^^Tw*\*^i< 


r  v.*  .*r 


83.     Radish  seedlings  grown  on  moist  sand,  showing  root-hairs. 

you  have  studied  the  main  root  and  the  side  roots. 

From  the  main  root,  the  side  roots  and  the  rootlets, 
spring  root-hairs;  these  can  be  seen  in  great  profusion 
if  we  sow  Radish  seeds  on  moist  earth  in  a  pan_  (Figs. 
83  and  84),  and  cover  it  with  a  piece  of  glass  to 
retain  the  moisture.  Sometimes  the  roots  become 
covered  with  mould,  w^hich  may  at  first  be  mistaken  for 
root- hairs.  The  best  way  to  obviate  this  is  to  obtain 
clean  seed;  if  this  is  not  possible,  rinse  the  dry  seeds 


(^ 


102 


KXPKNTMhJyrSl    W fTH   PLANTS 


a  few  moments  in  five  per  cent  formalin  and-  then 
rinse  in  clean  water;  heat  the  moist  earth  in  the  pan 
(which  should  be  covered  during  the  operation)  so 
that  it  steams  for  ten  or  fifteen  min- 
utes; allow  it  to  cool  and  then  place 
the  seeds  upon  it.  While  the  root- 
hairs  are  growing,  the  glass  cover 
should  not  be  disturbed. 

Does  the  amount  of  moisture  affect 
the  luxuriance  of  growth  of  the  root- 
hairs?  Use  a  series  of  pans,  with 
the  soil  varying  from  wet  to  fairly 
dry.  The  seeds  should  be  well 
soaked  when  placed  in  the  pans;  the 
moisture  in  each  pan  can  be  regu- 
lated by  lifting  the  glass  cover  so  as 
to  permit  greater  or  less  circulation 
of  air. 

What  is  the  use  of  the  root- hairs  ? 

The  absorptive  surface  of  the  root  is 

increased    many   fold    by   the    root- 

_____    _  _      hairs.     The  long,  feathery  root-hairs 

85.    Cutting  of  Wander-         whlcll     dcVClOD     OU    tllC    rOOtS     of     CUt- 
ing  Jew  in  water,  show-  ^ 

ing  root -hairs  which     tlugs  of  thc   Waudcriug  Jew  placed 

increase  the  absorbing  ^  <-"  -^ 

surface  from  fifty  to      \^  watcr  (Fig.  85)  iucrcasc  the  root 

seventy -five  times;  in  \        r>  / 

:;?£ce'°wT.ho"rrZl  surface  from  fifty  to  seventy  -  five 
S:wr,'h"avetb:  times;  to  get  so  much  surface  with- 
taTameVer,"""'*"     out    the    devlce   of   root-hairs   eacli 


THE    WORK    OF   ROOTS  103 

root  would  have  to  be  from  fifty  to  seventy- five  times 
thicker,  i.  e.,  from  an  inch  up  to  five  or  six  inches 
in  diameter. 

How  do  the  roots  (and  especially  root-hairs)  manage 
the  absorption  of  water  from  the  soil?  Do  they  find 
themselves  surrounded  by  water  ?  Tie  over  the  bottom 
of  a  lamp-chimney  (a  student-lamp  chimney,  size  No. 
1  is  very  good)  a  piece  of  cheese-cloth ;  fill  the  chim- 
ney with  soil  that  is  moist  enough  to  allow  good  plant- 
growth,  and  place  it  in  a  pan.  Pour  water  into  the 
pan  and  notice  its  rise  in  the  soil.  Are  the  spaces 
between  the  soil -particles  filled  with  air  or  with  water 
at  the  beginning  of  the  experiment  ?  Take  some  more 
moist  soil,  and  spread  it  out  on  a  thin  layer  on  a 
piece  of  paper.  Notice  the  glistening  appearance  of 
each  particle;  as  the  soil  dries  this  disappears  and 
the  particles  become  dull  in  appearance;  why?  If 
fine  gravel  is  used,  the  whole  process  is  very  easily 
seen.  It  appears,  then,  that  in  moist  soil  the  water 
is  in  the  form  of  thin  films  around  each  particle  and 
the  spaces  between  these  particles  are  filled  with  air; 
only  in  wet  soil  are  these  spaces  more  or  less  filled 
with  water. 

In  order  to  understand  how  the  root  absorbs  water 
from  the  soil,  we  must  understand  what  the  soil  is. 
Let  us,  therefore,  take  up  the  question,  Of  what  is  the 
soil  composed?^    Take  a  handful  of  earth,  rub   it  up 

iSee  King:    "The  Soil." 


104  EXPEBIMENTS    WITH  PLANTS 

well  in  water  to  form  a  paste.  Place  it  in  a  fruit- jar, 
fill  the  jar  with  water,  fasten  the  cover  on,  shake  the 
jar  well  for  some  time,  and  then  allow  it  to  stand  until 
the  soil  settles  to  the  bottom.  Examine  the  soil  after 
it  has  settled.  The  coarse  material  on  the  bottom  is 
sand^  above  this  is  finer  material  consisting  mostlj^  of 
clay^  the  finest  particles  of  which  remain  in  suspension 
in  the  water,  making  it  turbid.  On  the  top  of  the 
water  floats  a  little  vegetable  matter  which  in  its  de- 
composed state  is  called  Immns,  These  three  constitu- 
ents of  the  soil  have  very  different  properties,  which 
should  be  clearly  understood,  since  the  entire  fertility 
of  the  land  depends  on  a  proper  admixture  of  these 
constituents.  A  more  complete  separation  may  be 
effected  by  first  skimming  off  the  vegetable  matter,  then 
shaking  up  the  soil  again  in  water  and  pouring  the 
turbid  water  through  a  cloth.  Continue  the  process 
until  the  clay  is  all  removed  :  the  sand  will  remain  in 
the  bottom  of  the  jar.  A  still  better  separation  may  be 
effected  by  siphoning  water  from  a  pail  through  a 
piece  of  rubber  tubing  into  a  tumbler  (with  vertical 
sides)  which  contains  earth  (this  should  be  constantly 
stirred  with  a  pencil  during  the  passage  of  the  current) ; 
the  current  may  be  regulated  by  compressing  the 
rubber  tubing;  the  overflow  from  the  tumbler  should 
be  caught  in  a  second  tumbler,  of  larger  size,  placed 
beneath  the  first.  Beginning  with  a  weak  current,  the 
finest  particles  will   be   carried   over  into  the   second 


THE    WORK    OF  ROOTS  105 

tumbler.  When  this  has  been  accomplished  and  the 
water  runs  clear,  remove  the  second  tumbler,  substi- 
tute another,  and  increase  the  strength  of  the  current. 
By  continuing  in  this  way  the  soil  may  be  separated 
into  numerous  portions,  in  each  of  which  the  size  of  the 
particles  will  be  confined  within  certain  limits.  The 
time  which  the  particles  require  for  settling  in  these 
various  portions  is  of  importance.  Make  notes  on  this 
point. 

Sand. — Sand  is  made  up  of  larger  particles  than  clay, 
as  may  easily  be  seen  in  the  experiments  just  described : 
the  diameter  of  the  particles  ranges  from  .00004  inch 
to  .001  inch  and  larger.  Sandy  soils  are  usually  called 
"light"  because  they  are  more  easy  to  work,  although 
a  cubic  foot  of  dry  sand  weighs  one  hundred  and  five  to 
one  hundred  and  ten  pounds,  while  a  cubic  foot  of  dry 
clay  weighs  only  seventy  to  eighty  pounds.  Test  this 
statement.  They  are  more  open,  more  porous,  warmer 
and  drier  than  clay  soils.  Pure  sand  contains  practi- 
cally no  plant -food  ;  it  comes  from  quartz  rocks  ;  the 
purest  sand  consists  of  practically  nothing  but  particles 
of  quartz  which  have  a  very  characteristic  appearance 
under  the  microscope.  In  order  to  examine  sand  micro- 
scopically, breathe  on  a  slide,  place  a  little  sand  on  it 
and  then  turn  it  up  edgewise  so  that  all  the  sand  falls 
off,  with  the  exception  of  a  few  .scattered  grains  which 
adhere  to  it.  Examine  in  the  ordinary  way  with  the 
aid  of  the  mirror,  giving  a  bright  background,  and  also 


106  UXPEBIMAWTS    WITH   PLANTS 

without  the  mirror,  giving  a  dark  background:  use  the 
low  power  of  the  microscope. 

Clay. — Clay  is  mostly  made  up  of  particles  less  than 
.00004  inch  in  diameter  ;  the  particles  have  a  tendency 
to  cling  together  and  become  cemented  with  sand-parti- 
cles so  as  to  form  aggregate  particles,  or  soil-crumbs, 
which  may  be  of  much  larger  size  than  the  particles  of 
sand.  A  clay  soil,  therefore,  varies  greatly  in  charac- 
ter, depending  upon  the  degree  of  aggregation  of  its 
particles  and  its  content  of  sand.  In  drying,  clay  tends 
to  form  a  hard,  compact  mass  which  plant-roots  cannot 
penetrate.  When  it  becomes  wet  it  is  apt  to  assume  a 
greasy,  sticky  texture,^  impervious  to  water  and  im- 
penetrable to  plant-roots.  In  this  state  it  may  be 
further  compacted  by  chemical  agents,  by  kneading  or 
by  pressure,  to  form  Jiardpan,  which  is  really  soil  re- 
verting to  rock.  Hardpan  may  also  be  formed  of  com- 
pacted gravel.  Clay  lands  are  usually  said  to  be  heavy, 
stiff  and  cold  :  the  first  two  terms  refer  to  the  fact  that 
they  are  difficult  to  work,  the  last  to  the  fact  that  they 
contain  more  water  than  sandy  soils.  Clay  is  usually 
the  part  of  the  soil  richest  in  plant -food  :  it  results 
from  the  decomposition  of  rocks  containing  feldspar. 
Examine  some  dry  powdered  clay  under  the  microscope: 
do  you  find  aggregate  particles?  are  the  particles  of 
different  colors?    Find  out  what  you  can  about  them. 

1  How  do  the  properties  of  burnt  clay  differ  from  those  of  unburnt  clay  ? 
Why  1  Why  does  burning  clay  land  improve  it  ?  How  is  the  operation  carried 
out? 


THE     WO  UK    OF   h'OOTS  107 

The  experienced  eye  easily  distinguishes  between  the 
particles  of  hornblende  (which  are  black) ,  those  of  mica 
(which  are  brownish)  and  those  of  quartz  and  feldspar, 
which  are  both  of  light  color  but  differ  in  form. 

Humus. — Examine  a  little  leaf- mold:  can  you  make 
out  its  nature?  Place  some  of  it  under  the  microscope: 
place  some  on  a  red-hot  shovel  for  some  minutes :  what 
change  takes  place  ?  Perform  the  same  experiment 
with  some  dark  colored  soil :  does  it  change  color  ?  The 
simplest  way  to  remove  all  the  humus  from  a  soil  is  to 
burn  it  thoroughly ;  we  then  find  that  the  dark  color  of 
the  soil  is  due  entirely  to  the  humus.  The  fact  that 
humus  burns  so  readily  recalls  the  origin  of  peat  and 
coal,  which  are  formed  from  humus:  find  out  what  you 
can  about  this.  Humus  gives  to  the  soil  a  loose,  open 
texture  such  as  we  see  in  leaf- mold  ;  it  makes  the  land 
"mellow"  and  gives  it  "heart";  it  retains  an  extra- 
ordinary amount  of  water  (up  to  nearly  twice  its  own 
weight)  and  is  rich  in  plant-food.  It  often  accumulates 
in  forests  to  considerable  depths.  In  ordinary  soils  hu- 
mus is  present  to  the  depth  of  three  or  four  feet  (i.  e., 
the  depths  to  which  the  roots  ordinarily  penetrate),  and 
this  part  of  the  soil  has  a  looser  texture  and  darker 
color  than  the  underlying  subsoil,  which  is  devoid  of 
humus. 

By  a  proper  admixture  of  humus,  sand  and  clay  we 
can  obtain  a  soil  of  any  desired  consistency  or  texture 
and  of  any  grade  of  fertility.     The  gardener  does  this 


108  EXPERIMENTS    WITH   PLANTS 

extensively,  the  farmer  to  a  lesser  degree.  The  gar- 
dener has  various  mixtures  for  various  purposes:  for 
plants  requiring  much  water  he  makes  a  clay  loam 
(loam  is  a  soil  containing  about  equal  parts  of  sand 
and  clay  mixed  with  humus:  a  clay  loam  contains 
more  clay  than  sand,  a  sandy  loam  more  sand  than 
clay) .  For  plants  which  require  but  little  water,  such 
as  Cacti,  he  makes  a  sandy  loam:  for  Ferns  he  uses  a 
soil  composed  very  largely  of  humus.  For  young 
plants  he  makes  an  open,  porous  soil,  which  he  re- 
places by  a  heavier  soil  as  they  grow  older.  In  this 
way  he  succeeds  in  raising  from  a  small  pot  of  soil  as 
large  a  plant  as  the  farmer  ordinarily  produces  by  the 
use  of  a  thousand  times  as  much  earth.  The  farmer 
is  much  more  restricted  in  this  respect,  but  he  mixes 
humus  with  the  soil  by  plowing  in  straw,  stable  ma- 
nure or  green  plants:  he  also  adds  ashes,  clay  or  sand 
to  the  soil  when  necessary. 

What  kind  of  soil  is  best  for  cuttings?  Why? 
Which  crops  need  a  lignt  soil;  which  a  heavy  soil? 
Classify  the  soils  of  your  region  according  to  the 
following  scheme: 

Sand 80  to  100  per  cent  sand 

Sandy  loam 60  to    80         **  " 

Loam 40  to    60         "  " 

Clay  loam 20  to    40         "  *' 

Clay Oto    20 

The  red  or  yellow  color  of  soils  is  due  to  the  iron  in 
them:   the  black  color  to  humus.     Point  out  any  differ- 


TEE    WORK    OF  BOOTS  109 

erences  you  can  in  the  crops  borne  by  the  different 
kinds  of  soils  in  your  region.  Examine  the  different 
soils  with  the  microscope  (as  described  above) :  find 
out  all  you  can  about  their  composition  and  method  of 
formation. 

How  is  soil  formed?  Wherever  there  are  rocks,  soil 
is  being  formed.  Most  rocks  tend  to  break  'Up  until 
they  are  completely  changed  to  soil.  Among  the 
agencies  which  bring  this  about  may  be  mentioned: 

(1)  The  mechanical  action  of  moving  water,  ice  and 
wind;  (2)  changes  of  temperature;  (3)  the  chemical 
action  of  air  and  water;  (4)  the  action  of  plants  and 
animals.    Find  out  what  you  can  about  these  agencies.^ 

Study  the  weathering  of  rocks  in  your  vicinity,  also 
of  building  materials  (including  stone,  brick,  cement 
and  mortar) ;  which  kind  of  building  material  weathers 
most  rapidly?  Why?  On  hillsides  and  mountains  the 
soil  can  be  seen  in  the  act  of  originating  from  the  rock 
which  lies  beneath  it;  such  soil  is  said  to  be  formed  in 
place.  In  valleys,  on  the  other  hand,  we  find  soil 
which  has  been  transported  from  the  hills  or  mountains 
by  ice  (drift  soils)  or  water  (alluvial  soils) .  Moving 
water  always  carries  some  soil  with  it,  and  later  on  de- 
posits it  as  the  current  slows  down.  This  can  be  seen 
in  any  stream  or  in  the  little  rivulets  which  are  formed 

^Consult  Bailey:  "Principles  of  Agriculture,"  Chapter  I;  Johnson:  "How 
Crops  Feed,"  Chapter  II;  Gaye:  "The  Great  World's  Farm,"  Chapters  I  to  VII; 
King:  "The  Soil,"  Chapter  I;  any  good  text-book  of  Physical  Geography; 
Darwin:  "The  Formation  of  Vegetable  Moiald  Through  the  Action  of  Worms.*" 


110  EXPEHIMEyTS    WITH   PLANTS 

everywhere  during  rains.  To  study  it  more  carefully, 
we  may  construct  a  trough  about  twelve  feet  long,  a 
foot  wide  at  the  bottom,  with  sides  six  inches  high. 
This  is  best  made  in  three  sections,  each  four  feet 
long,  fastened  together  end  to  end  by  strong  hinges,  so 
that  they  may  be  inclined  at  different  angles.  The 
lowest  section  should  be  level,  the  next  iiiclined  at  an 
angle  of  fifteen  or  twenty  degrees,  the  next  at  an  angle 
of  twenty -five  to  thirty -five  degrees.  Line  the  trough 
throughout  its  entire  length  with  a  piece  of  oilcloth 
twelve  feet  long  and  two  feet  wide:  at  the  lower  end 
gather  up  the  oilcloth  and  tie  it  firmly  to  a  piece  of 
hose,  which  will  serve  to  carrj^  off  the  waste  water. 
Leave  the  lowest  section  empty;  fill  the  next  section 
with  sand;  fill  the  highest  section  with  clay  (placed  in 
the  trough  in  a  dry,  powdered  condition)  or  a  mixture 
of  clay  and  sand  (the  clay  should  be  pulverized  and 
mixed  with  the  sand  while  dry) .  Attach  a  piece  of 
rubber  tubing  to  the  faucet  and  allow  a  small  stream 
of  water  to  trickle  down  the  entire  length  of  the 
trough.  The  clay  (or  mixture)  in  the  upper  part  of 
the  trough  will  behave  in  the  same  way  as  rock  (only 
the  action  will  ])e  much  more  rapid),  and  will  show" 
clearly  how  rock  is  sculptured  by  running  water;  how 
masses  of  it  become  detached  and  fall  off,  and  how  as 
these  are  carried  down  stream  they  lose  their  sharp 
edges  (this  occurs  especially  where  the  clay  overlaps 
the  sand).     If  different  layers  of  clay  (or  mixture)  are 


THJ^J    WORK    OF    JfOOrS  111 

colored  by  earth  colors  (obtainable  at  a  paint  store) 
and  placed  over  one  another  and  then  compressed  or 
moulded  so  as  to  form  folds  like  those  of  rock  (syn- 
clines  and  anticlines),  and  placed  in  the  upper  sec- 
tion, we  shall  be  able  to  see  clearly  how  the  water 
wears  its  way  down  through  different  layers  of  rock 
(the  layers  may  be  made  of  different  hardness  by  mix- 
ing in'  more  or  less  sand  so  as  to  imitate  harder  and 
softer  rock  layers).  In  the  second  section  we  shall  see 
landslides,^  terraces,  meanders,  oxbows,  bubbling 
springs  (where  an  obstacle  occurs),  and  all  the  other 
features  of  stream  action.  In  the  third  section  we  shall 
see  alluvial  fans  and  cones,  deltas,  beaches,  the  deposit 
of  coarse  materials  near  shore,  and  of  finer  materials 
further  out  and  all  the  features  of  lake  and  ocean  for- 
mations. Now  that  we  have  learned  something  of  the 
nature  of  the  soil,  let  us  investigate  further  the  manner 
in  which  it  retains  the  soil -water. 

What  becomes  of  the  rain  water  which  falls  on  the 
soil  ?  Fill  a  box  about  eighteen  inches  square  and  four 
inches  deep  with  sand.  On  the  surface  of  this  place 
a  layer  of  wet  clay;  smooth  it  carefully  so  as  to  leave 
no  cracks  and  bring  it  down  over  the  outside  edges  of 
the  box  so  as  to  completely  cover  the  sand.  Place  a 
quart  of  water  in  an  ordinary  garden  sprinkler  and 
slowly  sprinkle  it  on  the  surface  of  the  clay.     Collect 

iln  regard  to  all  these  features,  consult  any  of  the  standard  elementary 
text-books  of  Physical  Geograpliy. 


112  EXPERIMENTS    WITH  PLANTS 

the  water  by  means  of  a  piece  of  oilcloth  about  three 
feet  square  placed  beneath  the  box.  How  rapidly  does 
the  water  run  off?  How  much  remains  behind?  Place 
a  layer  of  moist  cotton  batting,  about  an  inch  thick 
(sawdust  or  sphagnum  moss  such  as  florists  use  may 
be  employed)  on  the  surface  of  the  clay,  and  repeat  the 
experiment.  Remove  the  clay  from  the  sand  and  re- 
peat the  experiment,  with  and  without  the  cotton.  In 
this  experiment  the  cotton  represents  a  covering  of 
vegetation  on  the  soil:  such  a  covering  retains  the 
water  in  precisely  the  same  way  as  the  cotton.  Com- 
pare as  well  as  you  can  by  observation  the  amounts  of 
rain  which  run  off  from  the  surfaces  of  the  following: 

Clay  soil  without  covering. 

Sandy  soil  without  covering. 

Soil  with  a  covering  of  turf. 

Soil  with  a  covering  of  tall  weeds  or  other  plants. 

Soil  with  a  covering  of  shrubs  or  trees. 

It  is  believed  that  the  floods  of  our  great  rivers, 
such  as  the  Mississippi,  could  be  wholly  averted  by 
preserving  the  forests  at  the  headwaters.  Find  out  the 
annual  damage  of  these  floods.  This  represents  the 
interest  on  the  sum  which  could  be  profitably  invested 
in  preserving  these  forests.  What  does  this  sum  amount 
to  ?  If  you  live  in  a  region  where  damage  by  flood 
occurs,  make  a  similar  estimate  for  your  own  region. 
When  it  is  not  feasible  to  reforest  these  areas,  the 
natural  growth  of  shrubs  and  undergrowth  should  be 


THE    WORK    OF   ROOTS  113 

encouraged  by  preventing  fires,  keeping  out  sheep,  etc.^ 
Such  a  cover  not  only  prevents  floods,  but  it  prevents 
the  washing  away  of  the  soil  on  hillsides  and  slopes : 
the  damage  to  good  farm  land  from  this  source  may 
assume  enormous  proportions  and .  it  is  exceedingly^ 
difficult  ever  to  remedy  it  or  restore  the  land  so 
ruined. 

The  water  which  runs  off  without  penetrating  the 
soil  is  called  the  runoff :  that  which  soaks  into  the  soil 
is  known  as  the  percolating  water. 

For  convenience  we  sometimes  divide  tlie  soil -water  into  three 
kinds  :  (1)  free  water,  which  flows  under  the  influence  of  gravity  and 
percolates  down  through  the  soil  ;  (2)  capillary  water,  which  is  held  in 
the  capillary  spaces  or  pores  of  the  soil  and  is  not  influenced  by  gravity 
but  moves  upwai'd  or  in  any  direction  where  the  soil  is  becoming  drier  ; 
(3)  hygroscopic  water,  which  is  so  firmly  held  as  a  film  around  each  par- 
ticle that  it  does  not  move  about  like  the  capillary  water  but  can  be  re- 
moved only  by  heating  to  the  boiling  point  of  water,  when  it  passes  off  as 
steam  :  the  driest  of  "air- dry"  soils  contains  considerable  hygroscopic 
water. 

In  what  kind  of  soil  is  percolation  most  rapid ;  in 
what  kind  of  soil  is  water  retained  longest  after  a  rain  ? 
Fill  two  chimneys  as  described  above  — one  with  clay, 
the  other  with  sand;  put  them  in  separate  pans.  Pour 
an  equal  quantity  of  water  into  each  chimney,  taking 
care  that  none  runs  over;  through  which  does  the 
water  run  more  rapidly  I    Why  ?    Which  kind  of  soil 

1  Consult  Roth,  "First  Book  of  Forestry,"  pp.  202-209:  also  Tunmey, 
« Relation  of  Forests  to  Stream  Flow,"  Year-Book  of  the  U.  S.  Dept.  of  Agricul- 
ture for  1903. 


114 


EXPi':uiMi':xTs   with  plants 


3.  Apparatus  for 
measuring  the 
rate  of  evapo- 
ration from  a 
satui-ated  soil. 


has  the  larg'er  pai'tiek'.s;    the  hirger  spaces;    does  this 

explain  the  matter!  An  inch  of  rain  is  said  to  pene- 
trate four  inches  in  clayey  soil  and  six  to 
eight  inches  in  sandy  soil.  What  do  you 
think  of  this  statement  ?  Does  air  in  the 
soil  hinder  percolation  ? 

What  becomes  of  the  rain-water  which 
percolates  down  through  the  soil ;  is  any  of 
it  drawn  back  up  again  as  the  surface  dries? 
Prepare  a  bent  tube  as  shown  in  Fig.  ^Q^ 
one  arm  being  about  eighteen  inches  long 
and  the  other  about  four  inches.  Push  a 
little  wet  cotton  nearly  to 

the   bottom  of  the    longer   arm;    fill 

this  with  clay;  fill  the  longer  arm  of 

a  similar  tube  with  sand.     Attach  a 

funnel,  as  shown  in  Fig.  87,  and  pom- 
water  upon  the  soil  in  each  tube  until 

the  shorter  arm  of  the  tube  is  partly 

filled;    when  it  stops  rising,  remove 

the  funnel  and  pour  a  few  drops  of 

oil  on  the  surface  of  the  water  in  the 

shorter  arm  of  the  tube,  to   prevent 

evaporation.     Mark   accurately  on  a 

strip  of  paper   gummed   to  the  tube 

the  height  of  the   water -column   (it 

should    be   about  the    same  in   botli    8?.  Method  of  supplying 

.      ,  .  Ti>     j^i  j^  n    ^^         '  2.^  water  to  the  apparatus 

tubes).      It  the    water   tails    m    the      shown  in  Fig. so. 


THi:    WORK    OF   ROOTS 


115 


shorter  arm,  it  shows  that  some  of  the  water  which 
has  run  down  through  the  soil  is  being  drawn  up  again. 
In  which  tube  does  this  take  place  more  rapidly  ?  Is 
it  hastened  by  putting  the  tubes  in  the  sun?  Explain. 
It  often  happens  that  a  bed  of  gravel  lies  from  three 
to  six  feet  below  the  surface  of  the  soil ;  how  does  this 
affect  the  upward  move- 
ment of  water  in  the  soil  ? 
Place  a  little  gravel  in  the 
tube  and  note  the  effect. 

To  retain  the  moisture 
in  the  soil,  the  farmer  re- 
sorts to  cultivation  and 
mulching,  i.  e.,  placing 
on  the  surface  of  the  soil 
something  (straw,  dead 
leaves,  stable  manure, 
etc.)  to  prevent  evapora- 
tion. 

Take  four  student-lamp  chimneys  (Fig.  88),  cork 
them  securely  at  the  bottom  and  fill  them  with  good 
moist  soil  (which  should  be  previously  well  mixed  so 
as  to  be  uniform  throughout) .  On  the  top  of  the  soil 
in  one,  place  a  layer  of  dry  sawdust  four  inches  deep 
(a) ;  in  another  place  a  similar  layer  of  sifted  dry 
soil  not  packed  down  (/>) ;  in  another  plant  Wheat 
(c),  and  leave  the  last  as  a  control  {d) .  Weigh 
each  of  them,   and  repeat  the    weighing  at   intervals 


88.  Four  lamp-chiiinieys  filled  with  soil  for 
the  purpose  of  studying  the  rate  of  evap- 
oration from  the  surface:  (a)  surface 
covered  with  a  mulch  of  sawdust;  (ft) 
surface  tilled;  (c)surface  planted;  {d) 
control. 


116 


EXPERIMENTS    WITH    PLANTS 


of  a  week.     Which  loses  the  most  water;    the  least? 
Explain. 

The  result  of  cultivating  the  soil  is  to  keep  a  layer 
of  loose,  dry  soil  on  top,  which  acts  like  the  saw- 
dust in  preventing  evaporation,  by  reason  of  the  fact 
that  its  large  capillary  spaces  cannot  take  the  water 
from  the  smaller  spaces  of  the  underlying  soil.  This 
is  further  illustrated  by  the  fact  that  a  dry  brick  will 
take  water  from  a  moist  sponge,  but  a  dry  sponge  will 
not  take  up  water  from  a  moist  brick:   it  may  be  said 

that  the  surface  crust 
energetically  draws 
the  water  away  from 
the  underlying  soil, 
just  as  a  brick  will 
suck  a  sponge  dry. 
It  is  often  noticed 
that  where  the  soil 
has  been  well  tilled 
every  wagon-track  or 
footprint  remains 
moist  after  the  soil 
around  has  become 
dry,  and  weeds  spring 
up  noticeably  in  such 
places    owing   to   the 


88a.  New  growth  on  Apricot  trees  growing  side 
by  side.  Above,  the  cultivated;  below,  the 
uncultivated, 


fact    that    the    com- 
pressed soil  maintains 


TEE    WORK    OF   ROOTS  117 

capillary  connection  with  the  moist  earth  below. 
How  a  surface  layer  of  loose,  dry  soil  conserves 
moisture  is  well  seen  in  Fig.  ^^a^  which  shows  the 
new  growth,  during  one  summer,  of  two  trees  side  by 
side  under  the  same  conditions,  except  that  in  one  case 
the  ground  was  cultivated  while  in  the  other  it  was  not. 

The  loose,  dry  layer  of  earth,  known  as  the  surface 
mulch,  must  be  maintained  by  cultivating  the  surface 
as  often  as  it  becomes  baked  into  a  crust.  The  surface 
mulch  not  only  prevents  evaporation  but  it  admits  air 
(which  is  excluded  by  the  crust) .  It  prevents  the  soil 
from  cooling  oif  quickly  at  night  and  keeps  it  from 
freezing  deeply  in  winter  (snow  acts  as  a  mulch) .  It 
also  prevents  rain  from  running  off  the  surface.  In 
view  of  these  facts,  the  advice  "Water  your  garden 
with  the  rake"  becomes  important:  i.e.,  as  soon  as  the 
water  has  sunk  into  the  ground  go  over  it  with  a  rake 
and  break  up  the  surface  crust  so  as  to  foi-m  a  mulch. 

(What  connection  is  there  between  evaporation  from 
the  soil  and  the  formation  of  dew  ?  Invert  a  small 
tumbler  on  the  surface  of  moist  soil  and  leave  it  over 
night.  Are  you  able  to  find  any  dew  on  the  glass  the 
next  morning?  Why  is  dew  ordinarily  formed  only 
at  night  and  more  copiously  in  absence  of  wind  or 
clouds?) 

Is  all  of  the  rain-water  which  soaks  down  through 
the  soil  drawn  back  up  again  ?  How  are  springs 
formed?    How  deep  must  we  go  before  we  find  wet 


118  H^XPERIMENTS    WITH  PLANTS 

soil,  i.  e.,  soil  in  which  the  spaces  are  filled  with 
water  instead  of  air  I  This  level  is  called  the  water- 
table;  does  the  height  of  water  in  a  well  indicate  this 
point  reliably  ?  From  how  great  a  depth  is  the  water 
drawn  up  by  the  soil  ?  Get  a  glass  tube  about  six 
feet  long,  or  make  one  by  joining  together  short 
lengths  by  means  of  rubber  tubing.  Fill  this  with 
clay  (dried  and  pulverized),  and  place  the  lower  end 
in  water;  it  may  be  several  weeks  before  the  water 
stops  rising.  Clay  lifts  further  than  sand,  because  the 
spaces  between  the  particles  are  smaller,  but  it  cannot 
apparently  lift  more  than  six  feet.^  This  means  that 
practically  all  water  which  sinks  five  or  six  feet  below 
the  roots  of  a  plant  is  permanently  lost  to  that  plant. 
Moist  soil  draws  up  water  more  rapidly  than  dry,  but 
can  lift  it  no  higher. 

Find  out  what  you  can  about  the  height  of  the 
water-table  in  your  vicinity  at  various  seasons  of  the 
year;  does  it  follow  exactly  the  elevations  and  depres- 
sions of  the  surface  of  the  land  ?  How  many  feet  does 
it  rise  and  fall  yearly  ?  What  is  the  ideal  depth  for  the 
water-table?  Does  the  rise  of  the  water-table  in 
spring  help  to  thaw  out  the  ground  ? 

From  these  experiments  it  appears  that  in  soil 
which  is  moist  and  in  good  condition  for  growing 
plants   (but  not  wet)    the  water  exists  in  the  form  of 

iThe  finest  silt  may  lift  water  as  high  as  ten  feet:  this  necessarily 
occupies  a  very  long  time. 


THE    WORK    OF   BOOTS 


119 


drops  which  are  held  in  the  angles  between  adjacent 
soil  -  particles  (see  Fig.  89,  which  represents  a  fairly 
dry  soil) ;  it  also  forms  a  very  thin  film  on  the  surface 
of  each  particle.  The  re- 
maining space  is  filled 
with  air. 

The  water  causes  the 
soil -particles  to  adhere  to 
each  other,  just  as  two 
glass  plates  do  when  wet. 
or  the  hairs  of  a  brush 
dipped  in  w^ater. 

We  may  picture-  the 
relations  of  the  root-hairs 
to  the  soil -particles  by 
the  aid  of  Fig.  90,  in 
which  the  soil -particles 
(sp)  are  represented  as 
surrounded  by  water,  as 
shown  by  the  contour  lines  ;  this  represents  a  wet 
soil  containing  the  maximum  amount  of  water  in 
which  plants  can  grow.  Here  and  there  air- bubbles 
(a)  occur  which  furnish  the  root  with  oxygen.  The 
root-hairs  absorb  water  whenever  they  come  into  con- 
tact with  it  ;  this  causes  more  water  to  flow  from 
neighboring  particles  not  actually  in  contact  with  the 
root -hair.  In  this  way  each  root-hair  drains  a  con- 
siderable   extent    of    territory.       The    absorbed    water 


Diagram  of  a  fairly  dry  soil,  showing 
the  relations  of  a  root-hair  (rh)  to  the 
surrounding  soil -particles  (sp) .  The 
water  (iv)  is  held  in  the  form  of  small 
drops  (menisci)  between  the  angles  of 
adjacent  particles;  the  water  also  forms 
a  very  thin  film  on  the  surface  of  each 
particle,  as  well  as  on  the  surface  of  the 
root-hair.  The  remaining  space  is  oc- 
cupied by  air  (a). 


Cross-section  of  a  root,  as  it  grows  in  the  soil,  showing  the  relations  of  the 
root-liairs  (rh)  to  the  soil-particles  (sp)  and  the  air-spaces  (a):  this  soil  is 
represented  as  containing  the  maximum  amount  of  water  compatible  with 
good  plant-giowth.  Whenever  a  root-hair  absorbs  water,  more  flows  toward 
It  from  the  surrounding  region;  a  single  root -hair  is  thus  enabled  to 
drain  a  considerable  area.  The  water  absorbed  by  the  root-hairs  passes 
throngh  the  loose  outer  rind  or  cortex  of  the  root  to  the  wood-cells  (shown 
as  four  groups  of  thick-walled  cells  in  the  center  of  the  root);  alternating 
with  the  four  groups  of  wood-fells,  are  four  groups  of  thin-walled  bast,  while 
m  the  center  is  pith. 


THE    WORK   OF  ROOTS  121 

passes  through  the  root-han*  and  the  soft  outer  part 
(rind  or  cortex)  of  the  root  to  the  woody  strands 
in  the  center  (shown  in  the  figure  as  four  groups  of 
thick-walled  cells),  and  by  means  of  these  up  into  the 
stem.  (The  four  groups  of  thin -walled  tissues  alter- 
nating with  the  wood  are  the  bast;  in  the  center, 
surrounded  by  the  wood  and  bast,  is  the  pith.) 

Do  the  root-hairs  attach  themselves  closely  to  the 
particles?  Place  some  well- soaked  seeds  (Radish  seed  is 
especially  good)  on  the  surface  of  fine,  moist  gravel  in 
a  pan;  over  this  lay  a  piece  of  glass  to  retain  moisture. 
In  two  or  three  days  the  roots  will  be  covered  by  a 
thick  felt  of  glistening,  white  root-hairs.  As  they  come 
into  contact  with  the  particles  of  gravel  they  become 
firmly  attached  to  them.  When  this  has  happened, 
lift  the  seeds;  are  the  attached  particles  lifted  with 
them;  how  large  a  pebble  can  be  lifted  in  this  way; 
when  the  pieces  are  too  large  to  be  lifted  does  the 
root -hair  loosen  its  hold  or  does  it  break,  leaving  a 
portion  attached  to  the  particle  ?  What  conclusion  do 
you  draw  as  to  the  closeness  and  firmness  of  the 
attachment  ? 

In  dry  soil  the  water  exists  in  the  form  of  innumer- 
able little  reservoirs,  which  must  be  tapped  by  the 
root -hairs.  To  remove  the  water  some  force  must  bo 
used,  for  the  water  adheres  quite  firmly  to  the  soil- 
particles.  Not  only  must  the  reservoir  be  tapped  but 
the  water  must  be  drawn  forciblv  from  it.     How  does 


122  EXPEEIMENTS    WITH  PLANTS 

the  root-hair  pull  the  water  away  from  the  particles  ? 
It  would  seem  that  there  must  be  substauees  in  the 
root -hair  wliicli  attract  water,  just  as  the  sugar  draws 
the  water  through  a  Wahiut-shell  or  bladder  (pages  16 
and  61) .  In  some  roots  we  can  taste  sugar  (Carrot, 
Parsnip,  Beets,  etc.);  by  applying  chemical  tests  we 
find  in  all  roots  sugar  or  other  substances  capable  of 
attracting  water.  It  appears,  then,  that  the  root-hair, 
which  is  a  long,  closed  sack  (as  you  may  easily  see 
with  a  good  hand-lens  or  with  the  low  power  of  a  com- 
pound microscope),  contains  substances  w^hicli  attract 
water.  We  can  easily  make  an  artificial  root-hair ^  of 
any  sort  of  membrane  which  will  allow  water  to  pass 
through  but  retain  the  sugar  inside;  such  are  ox-  or 
pig-bladder  or  parchment  paper;  perhaps  the  most 
convenient  is  the  membrane  which  lines  an  egg-shell; 
empty  the  contents  of  the  e^g  through  a  small  hole  at 
one  end ;  jilace  the  shell  in  a  tumbler  and  cover  with 
weak  acid  or  vinegar;  place  another  tumbler  inside 
the  first,  to  keep  the  egg  submerged.  When  the  shell 
is  dissolved  away,  fasten  the  membrane  to  a  glass  tube 
(about  one-fourth  of  an  inch  in  diameter),  as  shown 
in  Fig.  91;  three  or  four  turns  of  tightly  wound  string 
(or,  better,  of   elastic  band)    fasten    it   satisfactorily.^ 

1  Artificial  root-hairs  may  be  made  by  hollowing  out  Carro^^s.  using  an  en- 
tire eg^,  etc.,  but  it  seems  better  to  eliminate  all  living  parts  from  the  appa- 
ratus, that  the  pui'ely  physical  features  may  be  emphasized. 

2  It  is  well  to  prepare  several  tubes  and  then  choose  the  one  which  gives 
the  best  results  on  trial. 


TIU]    WO  UK    OF    BOOTS 


123 


Place  it  under  water,  and  blow  gently  into  the  tube  to 
make  sure  there  are  no  leaks.  Pour  into  the  tube  enough 
strong  syrup  (sugar  and  water)  to  fill  it  to  f 
a  point  a  little  above  the  membrane.  Sub- 
merge the  membrane  in  water,  and  mark 
the  height  at  which  the  syrup  stands.  If, 
now,  this  artificial  root- hair  absorbs  water, 
we  can  detect  it  by  the  rise  of  fluid  in  the 
tube.  How  rapidly  does  it  rise  ?  How  far 
will  it  rise?  As  we  have  already  learned 
(pages  61  to  63),  the  absorption  of  water 
generates  pressure  inside  the  (closed)  arti- 
ficial root -hair.  In  the  real  root-hair 
pressure  is  generated  in  the  same 
way. 

What  happens  if  we  now  extract 
water  from  the  artificial  root-hair  by 
submerging  it  in  a  stronger  syrup 
than  that  which  is  inside  of  it  f  Pour 
sugar  into  the  tumbler  and  stir  it  un- 
til a  very  strong  syrup  is  formed; 
what  happens  to  the  liquid  in  the 
tube?  Try  the  same  experhnent  with  the  root-hairs; 
have  some  seedlings  with  good  root- hairs  growing  in 
water;  add  sugar  to  the  water  until  a  strong  syrup 
is  formed.  The  stiffness  of  the  root-hairs  is  due  ap- 
parently (like  the  stiffness  of  an  inflated  balloon  or 
bicycle  tire)   to  the  pressure  inside;  this  pressure   is 


91.  Artificial  root -hair, 
made  of  tlie  mem- 
l)raiie  whicli  lines  an 
egg-sliell. 


124  EXPERIMENTS    WITH  PLANTS 

due  to  the  absorption  of  water;  when  we  draw  this 
water  out,  the  root-hairs  collapse. 

Just  as  in  the  ease  of  the  seed  (see  page  18),  the 
presence  of  water- attracting  substances  (e.  g.,  salts, 
etc.)  in  the  soil- water  hinders  absorption  by  the  root; 
this  is  the  case  along  the  seashore  where  the  water 
is  brackish  and  in  alkali  soils. 

In  order  that  the  roots  may  be  able  to  explore  the 
soil  freely  and  absorb  water  from  it,  it  must  be  in  the 
proper  physical  condition  or,  to  use  a  more  common 
term,  it  should  be  mellow,  i.e.,  of  a  loose,  friable 
texture.  The  physical  condition  of  the  soil  is"  known 
as  tilth. 

How  may  the  soil  be  kept  in  good  tilth!  This  in- 
volves two  things:  (1)  keeping  the  soil-crumbs  of  the 
proper  size,  (2)  keeping  up  the  circulation  of  air  in 
the  soil. 

1.  The  size  of  the  soil-crumbs  is  of  the  greatest  im- 
portance. If  they  are  too  large,  the  surface  exposed 
to  the  action  of  the  roots  is  relatively  small.  Suppose 
chat  by  tillage  we  break  them  up  so  that  they  are  only 
one -tenth  of  their  original  diameter,  we  thereby  in- 
crease the  surface  available  to  the  roots  ten  times  and 
multiply  the  possibilities  of  plant-growth  accordingly. 
Soil  composed  of  too  large  crumbs  not  only  allows  the 
rain-water  to  leach  through  too  rapidly,  but  is  unable 
to  lift  it  up  again  to  any  great  extent  from  the  water- 
table. 


THE    WOBK   OF   ROOTS  125 

If,  on  the  other  hand,  the  crumbs  are  too  small,  the 
soil  becomes  impervious  to  water  and  wholly  unfit  for 
plant-growth:  this  is  the  case  with  the  finest  clays  or 
puddled  clay  soils.  As  already  explained,  the  surface 
mulch  of  larger- sized  crumbs  produced  by  cultivation 
conserves  the  moisture  of  the  soil  by  preventing 
surface  evaporation. 

2.  The  air  in  the  soil  is  kept  in  slow  but  constant 
circulation  by  the  fluctuations  of  barometric  pressure 
by  which  it  is  alternately  forced  into  the  soil  and 
sucked  out  again:  this  phenomenon  is  sometimes  so 
pronounced  that  the  air,  escaping  from  the  lower  strata 
of  soil  and  rushing  up  through  wells,  produces  a  loud 
noise,  causing  them  to  be  known  as  "whistling  wells." 
But,  despite  this,  it  is  necessary  to  stir  the  soil 
frequently  in  order  to  admit  air  if  we  wish  to  get  the 
best  results  from  crops.  The  great  importance  of  air 
as  an  agent  which  promotes  chemical  changes  in '  the 
soil  is  now  becoming  better  understood:  this  point  will 
be  discussed  later. 

The  necessity  for  a  supply  of  air  may  be  strikingly 
shown  by  placing  a  potted  plant  in  a  pail  of  water  so 
that  the  water-level  stands  a  little  above  the  top  of  the 
pot.  Note  the  appearance  of  the  plant  from  day  to 
day.  Alfalfa  fields,  if  flooded  for  two  or  three  days  in 
summer  time,  turn  yellow  and  the  plants  die.  Note  the 
effects  of  flooding  on  meadows  or  trees  whenever  an 
opportunity  occurs.     A  crust  on  the  surface  of  the  soil 


126  j!:xpEKiMEyTs  wite  plants 

excludes  air.  Paved  streets  and  sidewalks  often  cause 
injury  to  trees  by  preventing  access  of  air;  for  this 
reason  it  is  better  to  leave  an  open  space  about  them 
and  aerate  the  soil  by  frequent  cultivation.  We  fre- 
quently see  Willows  and  other  trees  on  the  banks  of 
streams  living  with  their  roots  completely  submerged  in 
water  or  in  saturated  soil ;  this  seems  at  first  glance  to 
be  in  contradiction  to  what  we  have  just  learned  about 


92.  Diagram  to  illustrate  the  effect  of  ideal  plowing.  The  compactness  of  the 
soil  is  indicated  by  the  density  of  the  shading.  Before  plowing,  there  is  a 
compact  surface  crust  («),  below  which  the  soil  grows  less  compact  as  we  go 
deeper;  after  plowing,  this  compact  muss  is  broken  up  into  a  loose,  friable 
mass  of  soil-criambs,  or  floccules,  with  a  consequent  increase  in  the  bulk  of 
the  furrow-slice  {fs)\  compacted  plow  sole  at  (pi).     (After  Hilgard.) 

the  necessity  for  a  supply  of  air  for  the  roots.  In  this 
case,  however,  the  roots  are  in  running  water  and  are 
able  to  make  use  of  the  small  but  continually  renewed 
supply  of  air  which  it  contains.  Where  the  soil  is  satu- 
rated with  water,  without  free  circulation,  the  air-sui)ply 
is  quickly  exhausted.  Not  only  are  the  roots  unable  to 
breathe  but  chemical  processes  injurious  to  the  plant 
are  set  up  in  the  soil. 

Plowing  and  surface  tillage  are  the  principal  means 
used  to  secure  good  tilth.  The  result  of  ideal  plowing 
is  shown  in  Fig.  92,  in  which  the  density  or  compact- 
ness  of  the    soil   is   indicated   by  the   density   of  the 


THJ^    WORK    OF    BOOTS 


12 


shading  (the  dots  ai-c  not  intended  to  represent  indi- 
vidual soil-particles  or  aggregations) .  At  {s)  is  the 
surface-crust,  which  may  become  very  hard  by  the 
baking  of  the  sun  and  the  beating  of  rain  upon  it,  as 
well  as  by  the  deposit  of  salts  which  are  left  behind  as 
the  water  evaporates.  In  soils  where  such  salts  are 
very  abundant  (alkali  soils)  they  form  a  whitish  deposit 
on  the  surface.  This  action  of  salts  may  be  very 
clearly  illustrated  by  placing  a  little  strong  eosin  solu- 
tion or  a  little  table  salt  in  the  bottom  of  a  tumbler 
and  then  filling  the  tumbler  with  wet  sand  and  allow- 
ing it  to  stand  in  the  sun  for  a  few  days. 

As  we  go  deeper  the  soil  becomes  less  compact  (as 
indicated  in  the  figure)  until  a  certain  depth  is  reached, 
when  it  begins  to  grow  more  compact  as  the  subsoil  is 
approached. 

The  plow  removes  a  slice  of  soil  and  inverts  it; 
in  ideal  plowing  the  in- 
verted portion  (called  the 
furrow  slice, /s)  is  left  in 
a  loose,  friable  condition. 
On  examining  it,  we  find 
it  broken  up  into  small 
rounded  masses  (soil- 
crumbs,  or  floccules),  as 
shown  in  Fig.  93.  Each 
one  of  these  masses  is  made  up  of  a  number  of  small 
soil -particles,    as    shown    in    Fig.    94,    which    repre- 


93.  Part  of  furrow  slice  (of  Fig.  92)  magnified 
to  show  floccules.  or  soil-crumbs. 


128 


EXPERIMENTS    WITH   PLANTS 


sents  a  single  soil -crumb  greatly  magnified.  The 
particles  are  held  together  by  the  water  {iv) ,  just  as 
are  two  plates  of  glass  or  the  hairs  of  a  brush  when 

wetted.  If  the  brush  be  dry  or 
submerged  in  water  the  hairs 
tend  to  fall  apart;  the  same  is 
true  of  the  soil-particles. 

At  the  same  time  that  the 
soil  is  broken  up  it  is  mixed  with 
air.  It  will  be  noticed  that  the 
surface  of  the  plowed  land  is 
much  higher  than  that  of  the 
nnplowed:  there  has  been  a 
noticeable  increase  of  bulk  due 
to  the  spaces  between  the  soil- 
crumbs  formed  by  tillage.  These 
spaces  are  filled  with  air,  so  that  the  increase  in  bulk 
represents  the  amount  of  air  which  has  been  mixed 
into  the  soil  in  the  plowing. 

Surface  tillage  is  accomplished  by  the  harrowing 
which  follows  plowing,  and  also  by  placing  the  plants 
in  rows  several  inches  apart  and  running  a  cultivator 
between  them.  This  serves  the  triple  purpose  of 
destroying  weeds,  breaking  up  and  aerating  the  soil, 
and  maintaining  a  surface  mulch. 

It  is  important  not  to  till  the  soil  when  it  is  too 
wet,  since  in  that  case  the  tendency  is  to  break  up  the 
soil -crumbs  into  their  constituent  soil -particles,  which 


A  single  soil -crumb  magni- 
fied to  show  the  soil-particles 
of  which  it  is  composed;  the 
particles  are  held  together  by 
the  water  (iv),  just  as  are  the 
hairs  of  a  brush  when  wetted. 
The  white  spaces  between  the 
particles  represent  air. 


THE    WOBK    OF   ROOTS  129 

results  in  the  formation  of  a  pasty  mass  impervious  to 
water,  as  can  be  easily  seen  by  kneading  a  little  wet 
clay.  Such  a  soil  is  called  a  puddled  soil,  and  its 
properties  are  illustrated  in  the  making  of  reservoirs, 
the  bottoms  of  w^hich  are  sometimes  lined  with  wet 
clay,  which  is  then  kneaded  by  driving  sheep  into  the 
enclosure:  the  result  is  a  layer  which  is  water-tight. 
To  a  certain  extent,  puddling  of  the  soil  is  caused  by  the 
beating  action  of  rain,  as  well  as  by  baking  in  the  sun 
and  the  deposition  of  salts  by  evaporation.  (Mulches 
prevent  this  action;  so  also  does  a  covering  of  plants, 
which  explains  why  the  soil  of  meadows,  natural 
pastures,  woodlands,  etc.,  remains  in  good  tilth.) 

It  is  interesting  to  note  that  puddling  may  also  be 
caused  by  tilling  the  soil  when  it  is  too  dry,  the  effect 
being  to  reduce  it  to  a  fine  powder,  which  forms  a 
pasty  mass  on  becoming  wet. 

Puddled  soil  is  improved  by  mixing  manure,  burnt 
clay,  straw,  coal  ashes  or  sand  with  it.  Try  an  experi- 
ment to  test  this.  The  addition  of  lime  is  also  beneficial, 
since  it  tends  to  form  floccules  (see  page  152). 

The  texture  of  the  soil  is  more  important  than  its 
richness,  and  it  is  almost  useless  to  apply  manures  to 
soil  which  is  in  poor  tilth:  tillage  is  of  more  importance 
than  manuring.^ 

1  See  King  :  "The  Soil,"  and  "Irrigation  and  Drainage":  Bailey  :  "Princi- 
ples of  Agriculture,"  Chaps.  II,  III  and  IV.  See  articles  in  the  Ycar-Book  of 
the  U.  S.  Dept.  of  Agriculture,  for  1894  by  Whitney,  Galloway  and  Woods;  for 
1895  by  Whitney  ;  for  1900  by  Briggs  ;  for  1903  by  King. 


130  EXPEIUMKXTS    WITH   PLANTS 

How  much  water  should  the  soil  contain  to  give  the  best 
results  in  growing  plants  ?  Take  five  tumblers,  fill  them 
with  soil:  add  to  the  first  15  cc.  of  water  each  day:  to  the 
second,  half  as  much ;  to  the  third,  half  as  much  as  to 
the  second,  etc.  Plant  the  same  number  of  Wheat-grains 
(or  other  seed)  in  each.  After  two  or  three  weeks  a 
great  difference  will  be  noticed:  those  which  receive  too 
much  water  will  not  grow,  on  account  of  lack  of  air  ; 
those  which  receive  too  little  will  suffer  from  drought. 
Somewhere  between  will  be  the  happy  medium  where 
the  plants  grow  best.  What  per  cent  of  water  does  this 
soil  contain !  We  may  ascertain  by  weighing  a  sample 
of  the  soil  and  then  drying  it  in  an  oven  and  weighing 
again.  For  practical  purposes  we  may  turn  the  ques- 
tion around  and  ask.  How  much  air  should  the  soil  con- 
tain ?  A  simple  method  of  answering  this  is  to  insert 
a  small  tube  to  the  bottom  of  the  soil,  connect  it  with 
a  funnel  and  then  pour  in  water  (from  a  receptacle 
containing  a  measured  quantity  of  water)  until  the 
water  stands  level  with  the  surface  of  the  soil.  Since 
the  water  displaces  the  air  in  the  soil  we  may  consider 
that  the  volume  of  water  poured  into  the  soil  represents 
approximately  the  amount  of  air  it  contained  :  this 
may  be  easily  compared  with  the  volume  of  the  soil. 

In  watering  gardens  and  potted  plants,  and  in  iri-i- 
gation  on  a  larger  scale,  it  is  important  to  know  how 
much  water  to  apply.  The  greatest  ignorance  prevails 
in  this  respect.    One   irrigator   will   use   ten   times  as 


THE    WOIiK    OF   HOOTS  131 

much  water  as  another  on  the  same  land  and  for  the 
same  crop  ;  house-plants  are  more  often  killed  by  in- 
judicious watering*  than  by  any  other  cause.  The 
greatest  harm  is  done  by  over -irrigation,  which  not 
only  drowns  the  roots  but  ruins  the  soil -tilth.  When- 
ever it  is  possible,  irrigation  should  be  done  by  means 
of  underground  pipes  or  drains  :  these  deliver  both 
water  and  air  to  the  roots  precisely  where  they  are 
needed,  and,  if  a  good  surface  mulch  be  maintained, 
there  is  almost  no  loss  by  evaporation.  This  method  is 
especially  adapted  to  greenhouses  and  intensive  horti- 
culture generally.  It  is  stated  that  by  this  system,  as 
practiced  in  the  open,  only  a  twentieth  part  of  the  or- 
dinary amount  of  water  needs  to  be  given  and  the  tilth 
of  the  soil  is  kept  in  the  best  condition,  while  the  sur- 
face of  the  land  is  left  free  for  tillage. 

The  amount  of  water  which  the  soil  should  contain 
to  give  the  best  results  will  vary  somewhat,  according 
to  circumstances  (some  plants  require  much  more  than 
others) .  In  general  the  soil  should  not  contain  more 
than  60  per  cent  of  its  water-holding  capacity,  i.  e.,  at 
least  two-fifths  of  the  spaces  should  be  occupied  by  air. 
The  water- holding  capacity  of  a  soil  may  be  deter- 
mined by  saturating  it  with  water,  draining  off  the 
surplus,  weighing  a  portion  of  it  and  then  drying  it  on 
a  water- bath  to  constant  weight.  The  loss  in  weight 
divided  by  the  dry  weight  gives  the  percentage 
of  water   (i.  e..,  water- holding    capacity  of  the   soil). 


132  EXPERIMENTS    WITH  PLANTS 

Compare  the  water- holding  capacity  of  sand,  clay  and 
humus  (leaf-mold). 

Air  reaches  the  roots  of  potted  plants  not  only 
from  above  but  also  through  the  sides  of  the  pot. 
How  permeable  the  latter  is  to  air  may  be  tested  by 
cementing  a  piece  of  it  to  a  glass  tube  and  proceed- 
ing as  in  the  experiment  shown  in  Fig.  28,  or  by  sim- 
ply placing  a  piece  in  an  air-pump  (see  page  187)  and 
exhausting.  The  outside  of  a  pot  should  be  washed 
occasionally  to  keep  it  clean  and  porous,  so  that  air 
may  enter  it  freely. 

To  retain  in  good  condition  the  soil  in  which  potted 
plants  are  grown,  they  should  not  be  watered  too  often, 
but,  w^hen  water  is  given,  it  should  be  applied  copi- 
ously (preferably  by  submerging  the  entire  pot  in  a 
pail  of  water) .  A  good  rule  is  to  water  about  once  a 
week  in  this  way  and  to  delay  watering  in  any  case 
until  the  pot  sounds  hollow  on  being  tapped.  The 
frequent  application  of  a  little  water  merely  wets  the 
top  layer  of  soil,  leaving  the  bottom  dry.  On  the 
other  hand,  too  much  water  deprives  the  roots  of 
air  and  causes  them  to  decay.  Devise  an  experi- 
ment to  determine  in  the  case  of  some  house  plants 
how  much  water  should  be  given. 

How  may  the  soil  moisture  be  regulated  ?  We  may 
answer  this  question  by  reviewing  what  has  already 
been  said.  (1)  Moisture  may  be  decreased  by  under- 
ground drains  or  by  plowing  land  without  subsequently 


TEL'    WORK    OF   BOOTS  133 

making  a  surface  mulch,  in  which  case  it  soon  dries 
out;  (2)  moisture  may  be  increased  by  a  surface  mulch 
which  hinders  the  rain-water  from  running  off  and 
largely  prevents  loss  by  subsequent  evaporation  ;  by 
keeping  the  soil  in  good  tilth;  by  the  addition  of 
humus ;  by  artificial  application  of  water. 

Other  things  being  equal,  the  yield  of  a  crop  is  di- 
rectly proportional  to  the  amount  of  water  it  receives 
within  the  limits  mentioned  above. ^ 

How  thoroughly  do  roots  explore  the  soil  for  mois- 
ture? This  may  be  investigated  by  carefully  re- 
moving the  earth  in  successive  layers,  or,  better  still, 
digging  a  trench  around  the  plant  and  lifting  out  a  large 
ball  of  earth,  which  should  be  carefully  washed  away 
by  means  of  a  hose.  The  roots  of  Corn,  Barley,  etc., 
examined  in  this  way  show  a  dense  mat  extending 
downward  three  or  four  feet.  In  a  root- system  of  this 
kind  we  find  practically  every  cubic  inch  of  the  soil 
explored  by  one  or  more  (sometimes  by  very  many) 
roots:  a  conservative  estimate  of  the  extent  of  the 
root- system  of  four  well -developed  Corn  plants  gave 
an  aggregate  length  of  over  a  mile  of  roots,  not  count- 
ing root-hairs.  The  estimate  was  made  by  calculating 
the  number  of  cubic  inches  of  soil  (the  roots  occupied 
a  cube  of  earth  a  little  less  than   three  and  one -half 

iSee  Bailey,  "Principles  of  Acrrieulture";  King,  "The  Soil"  and  "Irrigation 
and  Drainage";  also  articles  in  the  Year-Book  of  the  U.  S.  Dept.  of  Agriculture 
for  1895  by  Taft;  for  1898  by  Briggs;  for  1900  by  Johnson  and  Stannard; 
for  1902  by  Beals. 


134  EXPERIMENTS    WITH   PLANTS 

feet  on  a  side) ,  which  were  thoroughly  explored  by  the 
roots,  and  assuming  each  cubic  inch  of  earth  to  contain 
only  one  linear  inch  of  root.  The  entire  root -system 
of  a  Squash  vine  was  found  by  actual  measurement  to 
be  over  fifteen  miles  in  length  (not  counting  root- 
hairs),  and  of  this  length  the  major  part  must  have 
been  produced  at  the  rate  of  1,000  feet  per  day. 

The  spread  of  the  root  is,  in  general,  about  the 
same  as  the  spread  of  the  branches.  Thus  the  "feed- 
ing roots  "  (the  fine,  branching  roots  which  do  most  of 
the  absorbing)  of  a  tree  are  largely  located  beneath 
the  tips  of  the  branches  where  the  drip  of  the  rain 
and  dew  falls  directly  upon  them;  and  the  same  is 
true  to  a  great  extent  of  shrubs  and  herbaceous  plants. 
With  these  general  facts  in  mind,  it  will  be  of  interest 
to  investigate  a  few  special  cases,  especially  of  trees 
or  crops  common  in  your  region.  It  will  also  be  of 
interest  to  examine  the  behavior  of  the  roots  of  potted 
plants. 

As  a  rule,  the  roots  of  ordinary  crops  do  not  pene- 
trate the  soil  to  a  depth  of  more  than  three  or  four 
feet,  but  in  dry  regions  they  may  penetrate  ten  or 
twelve  feet  (or  more)  into  the  soil  in  the  search  for 
moisture;  in  consequence  of  this  they  are  enabled  to 
withstand  long  periods  of  drought.  Alfalfa  grown  in 
dry  soil  may  penetrate  more  than  twice  as  deep  as 
this.  Some  crops.  Grasses,  etc.,  are  known  as  "sur- 
face feeders."     Such  are  often  grown  in  orchards,  etc., 


THE    WORK    OF   BOOTS  135 

since  they  do  not  interfere  with  the  deeper  roots  of  the 
trees.  (Monocotyledons  are  mostly  shallow -rooted,  be- 
cause the  roots  spread  out  near  the  top.)  Others, 
for  the  opposite  reason,  are  known  as  "deep  feeders." 
It  is  of  the  greatest  importance  to  take  these  facts  into 
account  in  hoeing  and  cultivating  the  soil:  the  deeper 
the  roots  the  deeper  should  be  tlie  plowing  and  subse- 
quent cultivation.  It  is  of  importance  to  know  that 
by  proper  irrigation  it  is  possible  to  control  the  growth 
of  the  roots  so  as  to  cause  them  to  grow  deep  or  near 
the  surface:  the  more  the  soil  is  saturated  with  water 
the  nearer  the  surface  will  the  roots  stay,  on  account 
of  their  need  of  air.  Where  there  is  a  long  dry 
season  the  water-table  sinks  steadily:  if  the  crop  is 
planted  early  enough  the  roots  follow  the  water-table 
down  and  so  maintain  themselves,  but  if  planted  two 
or  three  days  too  late  they  are  unable  to  do  so  and  the 
plants  perish.  What  crops  stand  drought  best  ?  Are 
they  deep-rooted  plants? 

Cake  of  Roots. — When  roots  become  sickly,  water 
sparingly;  place  the  plant  in  a  cool,  shady  place, 
sprinkle  the  leaves  from  time  to  time  and,  if  necessary, 
prune  off  some  of  the  leaves  and  branches.  Under 
these  circumstances  the  plant  will  need  little  water 
(for  reasons,  see  page  212)  and  the  roots  will  have  an 
opportunity  to  recover. 

In  repotting  plants,  invert  the  pot  and  tap  smartly 
until  the  ball  of  earth  is  loosened.  On  removing  the  pot, 


136  EXPERIMENTS    WITE   PLANTS 

a  perfect  felt  of  roots  will  usually  be  found  next  the 
pot.  These  should  be  removed,  since  they  are  sure  to 
be  injured  in  any  case  and  their  subsequent  decay  may 
affect  the  rest  of  the  root.  Remove  the  outer  part  of 
the  ball  of  earth  (which  has  become  compact  and 
sour) ,  hold  the  plant  with  the  left  hand  at  the  proper 
height  in  the  new  pot,  and  with  the  right  hand  pack 
the  fresh  earth  about  the  roots.  The  pot  may  then  be 
immersed  in  water  until  bubbles  cease  to  rise. 

Trees  which  are  intended  for  transplanting  should 
have  the  roots  confined  to  a  small  space  by  transplant- 
ing and  root- pruning  once  a  year.  Trees  with  spread- 
ing roots  may  be  treated  as  follows:  Some  time  before 
the  tree  is  to  be  transplanted  a  trench  is  dug  about  it 
and  filled  with  good  earth.  From  their  cut-off  ends 
the  roots  will  send  out  new  rootlets  into  this  earth. 
When  this  is  accomplished  the  tree,  with  its  ball  of 
earth,  may  be  pulled  over  and  then  raised  by  a  suit- 
able tackle,  and  transported.  (In  addition  to  these 
precautions,  it  is  important  in  transplanting  trees  to 
see  that  the  points  of  the  compass  remain  in  the  same 
relation  to  the  tree  in  its  new  position,  i.  e.,  that  the 
north  side  shall  remain  the  north  side  after  transplant- 
ing; for  reasons,  see  page  220.) 

The  water  contained  in  the  soil  dissolves  out  from 
it  mineral  substances  (such  as  the  salt,  which  is  con- 
stantly carried  to  the  sea,  and  the  lime,  which  is  de- 
posited in  boilers,  tea-kettles,  etc.).    Are  these  mineral 


THE   WORK   OF  BOOTS  137 

matters  absorbed  by  the  plant  ?  We  may  easily  answer 
this  question  by  burning  the  plant,  since  whatever 
remains  after  thorough  burning  represents  mineral 
matters  which  have  been  absorbed  by  the  plant.  We 
first  dry  the  plant  thoroughly  in  the  sun  or  in  an  oven ; 
we  then  break  it  into  small  pieces,  place  them  on  a 
small  iron  shovel  and  heat  it  red-hot.  Continue  the 
heating  until  the  ash  becomes  white,  or  nearly  so,  on 
cooling. 

If  we  weigh  the  plant  before  and  after  drying,  and 
also  the  ash  left  after  burning,  we  shall  know  approxi- 
mately how  much  water,  how  much  cellulose  (see  page 
QQ)  or  woody  fiber  (the  combustible  part) ,  and  how 
much  mineral  matter  it  con- 
tains. 

Is  the  absorbed  mineral 
matter  of  use  to  the  plant  ? 
In  order  to  deprive  the  plant 
of  its  supply  of  mineral  mat- 
ter, we  must  furnish  it  with 
distilled  water  instead  of  or- 

T  i  TTT  1         95.     A  still    t'(u-  making  distilled  water: 

dmary  water.     We  may  ob-        it  consists  of  two  pans  and  a  cake- 

tain  distilled  water  by  means  *^"  ^^"  ""^  graniteware  or  tinware). 

of  the  apparatus  shown  in  Fig.  95.  It  consists  of 
two  pans  and  a  cake-tin,  the  central  cone  of  which 
has  been  shortened  to  the  proper  length  by  making 
vertical  cuts  with  a  pair  of  stout  shears  and  then  bend- 
ing back  the  flaps  as  shown  in  the  figure.     Water  is 


138  EXPERIMENTS    WITH  PL  A  XT  S 

placed  in  the  lower  and  upper  pans  and  the  whole 
apparatus  set  on  a  stove.  When  the  water  in  the 
lower  pan  boils  the  steam  rises  until  it  strikes  the 
under  surface  of  the  upper  pan,  which  is  kept  cool 
by  the  water  in  it.  The  steam  condenses  in  drops  and 
collects  in  the  cake- tin. 

It  is  desirable  to  use  graniteware  utensils  for  this 
apparatus,  but  tinw^are  is  equally  good  so  long  as  it 
is  kept  bright  and  free  from  rust.  Distilled  water  may 
be  made  in  this  apparatus  at  the  rate  of  over  a  quart 
an  hour.  The  cost  of  the  whole  apparatus  need  not 
exceed  half  a  dollar. 

The  purity  of  distilled  water  (like  that  of  "rain- 
water) depends  on  the  fact  that  when  water  evaporates 
it  leaves  behind  any  substances  w^hich  may  be  dis- 
solved in  it.  (We  may  use,  if  necessary,  freshly  col- 
lected rain-water  in  place  of  distilled  water.) 

Wheat  may  be  recommended  for  this  experiment. 
Place  the  seeds  in  boxes  of  sawdust;  water  one  with 
distilled  water;  the  other  w^ith  pond-,  river-  or  tap- 
w^ater  (giving  the  same  amounts  to  each).  We  may 
also  grow  the  plants  directly  in  water.  For  this  pur- 
pose slips  (about  eight  inches  long)  of  the  Wandering 
Jew  or  Inch  Plant  (Tradescantia)  may  be  recom- 
mended. The  slips  are  placed  in  fruit -jars  contain- 
ing about  two  quarts  of  water,  and  placed  where  they 
will  receive  about  the  same  amount  of  light  as  is 
needed  by  ordinary  house -plants.      We  may  carry  the 


THU    WORK   OF   ROOTS  139 

experiment  further  and  add  to  the  tap-water  various 
mineral  substances,  to  stimulate  the  growth  of  the 
plant.  Saltpeter  and  bone  superphosphate  (one  ounce 
of  each  dissolved  in  three  quarts  of  water)  may  be 
used  in  this  way.  Experiments  carried  out  in  this 
way  have  shown  that  the  mineral  matters  indispensa- 
ble to  the  plant  consist  of  four  bases  and  four  acids. 


hases  : 

Th 

e  acids  : 

Potash 

Nitric 

Lime 

Phosphoric 

Magnesium 

Sulphuric 

Iron 

Carbonic  (from  the  air 

If  we  dissolve  in  distilled  water  all  the  above  sub- 
stances (except  carbonic  acid) ,  plants  may  be  grown 
in  it  until  they  flower  and  fruit  and  produce  perfect 
seeds;  but  if  we  omit  any  of  the  elements  involved 
(except  carbonic  acid) ,  the  plant  soon  stops  growing 
and  fails  to  flower  or  fruit.  (Carbonic  acid  is  neces- 
sary to  the  plant  but  is  absorbed  from  the  air,  as  we 
shall  see  later.)  Fig.  96  shows  the  result  of  such  an  ex- 
periment made  with  the  Wandering  Jew  or  Inch  Plant. 

All  these  substances  must  exist  in  the  soil  in  order 
that  the  plant  may  thrive,  and  they  must  not  only 
exist  there  but  be  soluble  in  the  soil-water.  The  car- 
bonic acid  of  the  soil  is  of  great  service  to  the  j)lant, 
since  it  dissolves  many  substances  which  would  other- 
wise remain  undissolved.  If,  for  instance,  we  add  to 
lime-water  (which  has  been  filtered  clear)  a  little  soda- 


140 


EXPEBIMENTS    WITH  PLANTS 


water  (i.  e.,  water  highly  charged  with  carbonic  acid; 
it  is  bottled  under  pressure  and  sold  as  "plain  soda"), 
we  shall  get  a  milky  precipitate  or  sediment  of  car- 
bonate of  lime  (due  to  the  union  of  lime  and  carbonic 


96.  The  result  of  a  (five  weeks)  water  culture  of  Wandering  Jew:  the  one  marked  "full 
quota"  had  all  the  indispensable  food- substances  dissolved  in  the  water;  each  of 
the  others  lacked  one  element. 

acid).  On  adding  more  soda-water,  the  milky  ap- 
pearance vanishes  and  the  water  becomes  clear,  owing 
to  the  fact  that  the  carbonate  of  lime  has  been  dis- 
solved by  the  excess  of  carbonic  acid.  If  we  now 
heat  this  clear  water,  the  excess  of  carbonic  acid  will 
be  driven  off  (as   shown   by  the   constant   and   rapid 


THE    WORK   OF  BOOTS  141 

rising  of  bubbles) ,  and  the  milkiness  will  reappear  as 
the  carbonate  of  lime  separates  out  in  solid  particles. 

This  experiment  may  also  be  performed  by  stirring 
up  fine  marble  dust  or  whiting  (both  of  which  consist 
of  carbonate  of  lime)  in  a  little  water,  pouring  off  a 
little  of  the  milky  fluid  into  two  separate  tumblers  and 
adding  to  one  a  considerable  quantity  of  tap -water,  to 
the  other  the  same  quantity  of  soda-water.  Cover  each 
tumbler  with  a  piece  of  glass  and  set  them  aside,  to 
see  in  which  the  carbonate  of  lime  will  dissolve  first. 

Since  carbonate  of  lime  is  the  principal  constituent 
of  marble  and  limestone,  we  can  readily  understand  how 
these  rocks  are  dissolved  by  water  containing  carbonic 
acid  and  also  why  they  are  deposited  on  vessels  in  which 
such  water  is  boiled.  The  carbonic  acid  in  soil -water 
comes  mostly  from  the  decay  of  animal  and  plant  re- 
mains. It  dissolves  not  only  limestone, etc., but  practi- 
cally all  other  minerals  which  the  plant  uses  as  food. 

We  have  already  learned  (page  34)  that  seeds  give 
off  carbonic  acid ;  if  the  root  also  has  this  property  it 
must  be  of  very  great  advantage  to  it  in  dissolving  the 
plant-food  immediately  around  it.  Does  the  root  give 
off  carbonic  acid  ?  We  may  test  this  by  growing  roots 
in  lime-water.  Fill  two  similar  bottles  with  lime-water 
(filtered  through  filter  paper  or  cotton  wool) ,  and  cut 
in  the  cork  of  each  a  notch  large  enough  to  receive 
the  stem  of  a  seedling  plant  two  or  .three  inches  long 
(Peas,  Beans,  etc.,  grown  in  sawdust  answer  excel- 


142  EXPElilMENTS    WITH   PLANTS 

lently).-  Place  the  seedling  in  the  bottle  so  as  to  sub- 
merge the  roots,  and  tuck  a  little  cotton  around  the 
stem  of  the  plant  where  it  passes  through  the  cork. 
Arrange  the  second  bottle  in  the  same  way,  but  put  no 
plant  in  it;  simply  fill  the  notch  in  the  cork  with 
cotton.  If,  now,  the  roots  give  off  carbonic  acid  we 
shall  expect  to  find  the  lime-water  in  which  they  are 
submerged  turning  milky  after  a  time,  while  that  in  the 
control  bottle  remains  clear  (or  shows  a  slight  degree 
of  milkiness  due  to  the  carbonic  acid  of  the  air). 

In  order  to  get  a  better  idea  of  the  giving  off  of 
acid  by  the  root,  we  should  grow  some  roots  in  gela- 
tine to  which  litmus  has  been  added.  This  very  inter- 
esting experiment  may  be  performed  in  a  variety  of 
ways.  Some  of  the  so-called  "sparkling  gelatines" 
used  for  cooking  are  preferable.  Dissolve  one  part 
of  gelatine  in  about  five  parts  of  water.  This  is  most 
conveniently  done  by  letting  it  soak  in  cold  water  over 
night  and  then  putting  it  on  a  water-bath  (see  Figs.  51- 
and  206).  When  the  gelatine  is  dissolved,  add  enough 
litmus  dissolved  in  water  ^  to  give  the  gelatine  a  strong 
(reddish  purple)  color.  Now  add  lime-water  cau- 
tiously until  the  color  changes  to  blue.  The  gelatine 
should  now  be  filtered,  as  described  on  page  369,  and 
should  then  be  quite  clear.  Pour  some  of  it  into  white 
saucers  to  the  depth  of  a  quarter  of  an  inch;  when  it 
has  "set,"  take  some  Peas  (or  other  seeds,  with  straight 

1  Obtainable  at  druggists'. 


THE    WORK   OF  BOOTS 


143 


caulicles,  about  an  inch  long,  and  thrust  the  caulicles 
horizontally  into  the  gelatine  so  that  they  are  covered 
by  it;  arrange  several  seeds  in  a  saucer  in  this  man- 
ner, and  then  cover  it  with  a  piece  of  glass.  If  car- 
bonic (or  other  acid)  is  being  given  off  by  the  root,  we 
shall  be  able  to  detect  it  by  the  change  in  color  (from 
blue  to  reddish)  of  the  gelatine  around  it.  The  result 
will  be  most  apparent  if  the  color  of  the  gelatine  is 
as  pronounced  as  possible  without  being  strong  enough 
to  make  it  opaque. 

A  still  better  method  is  to  stop- 
per the  neck  of  a  small  glass  fun- 
nel at  the  lower  end  with  a  small 
cork,  and  then  pour  in  the  gela- 
tine until  the  neck  is  completely 
filled.  A  Pea  with  a  straight  caul- 
icle  may  then  be  placed  in  the  fun- 
nel with  the  caulicle  directed  down- 
ward into  the  neck  and  submerged 
in  the  gelatine.  The  funnel  should 
then  be  covered  with  a  piece  of 
glass,  to  retain  moisture  (Fig.  97), 
and  may  be  conveniently  supported 
in  the  manner  shown  in  the  figure. 

A  simpler  method  is  to  use  ordinary  blue  litmus 
paper,  folded  as  for  filtering  and  placed  in  a  funnel, 
which  is   then   filled   with   earth  ^  in  which   seeds   are 


App.iiJitiis  to  (letcniiiiie 
whether  the  root  excretes 
acid;  the  root  is  growing 
in  gehitine  which  has  been 
colored  bhie  by  the  addi- 
tion of  litmus. 


1  The  action  of  the  soil  on  litmus  paper  must  be  tested,  since  sour  soils 
will  redden  it. 


144  EXPERIMENTS    WITH    PLANTS 

planted,  as  shown  in  Fig.  82.  Water  it  until  the  roots 
have  grown  down  along  the  litmus  paper;  then  cease 
watering.  In  the  course  of  a  day  or  so  the  result 
should  be  plainly  visible.  This  method,  while  sim- 
pler, is  much  less  beautiful  than  the  preceding. 

Another  way  for  testing  the  roots  for  excretion  of 
acids  is  to  obtain  a  piece  of  polished  marble,  on  which 
is  placed  a  layer  of  moist  sand  about  an  inch  deep, 
in  which  seeds  are  placed.  As  their  roots  come  in 
contact  with  the  marble  they  should,  if  they  excrete 
enough  acid  and  the  time  is  sufficient  (two  to  six 
weeks),  produce  a  slight  etching  of  the  polished  sur- 
face; if  such  etching  occurs  it  may  be  made  more 
striking  to  the  eye  by  rubbing  powdered  graphite 
(obtained  by  scraping  the  lead  of  a  pencil)  on  the  mar- 
ble. It  is  often  more  convenient  to  use  a  seedling  with 
a  stout  root  (Bean,  Scarlet  Runner  or  Pea),  which  is 
laid  directly  on  the  polished  marble,  covered  with  wet 
filter  paper  which  dips  into  a  dish  of  water  and  is 
pressed  down  by  laying  a  piece  of  glass  over  it.  In 
place  of  marble  we  may  use  a  mixture  of  equal  parts  of 
plaster  of  Paris  (previously  well  heated)  and  whiting 
(or  fine  marble  dust)  rubbed  up  together  in  water 
and  then  poured  out  on  a  piece  of  glass  and  allowed 
to  harden:  if  this  be  carefully  removed  from  the 
glass  the  surface  will  have  sufficient  polish  for  the 
purpose. 

Roots  are  able  to  decompose  even  the  hardest  rocks, 


THE    WOBK   OF  BOOTS  145 

such  as  lava  and  basalt,  though  of  course  much  more 
slowly  than  soft  rocks,  such  as  limestone,  etc. 

Clay  (which  consists  of  alumina  combined  with 
silica  and  water)  is  of  great  service  to  the  plant  in 
"fixing"  plant -foods.  We  may  illustrate  this  by  filling 
a  lamp-chimney  with  clay  or  good  garden  soil  (so 
firmly  packed  that  the  liquid  takes  an  hour  or  so  to 
run  through)  then  pour  in  ammonia  water  at  the  top; 
the  water  will  be  deprived  of  the  ammonia  in  passing 
through  the  soil  and  will  come  out  at  the  bottom  with- 
out any  odor  of  ammonia.  The  ammonia  has  been 
"fixed"  (principally  by  the  compounds  of  alumina)  in 
the  soil  so  that  it  cannot  be  readily  washed  out  by 
rain,  etc.  The  same  thing  happens  with  dung  liquor, 
phosphoric  acid  (fixed  by  lime  and  magnesia  and,  to  a 
slight  extent,  by  iron  in  the  soil)  or  potash  (for  the 
last  two,  test  with  litmus  paper) . 

The  carbonic  acid  of  the  soil  and  the  alumina 
and  silica  of  the  clay  act,  not  as  foods  of  the  plant,  but 
as  servants  w^hich  store  food;  the  clay  (and  likewise 
humus)  "fixes"  soluble  food  which  would  otherwise  be 
washed  out  of  the  soil  by  the  rain,  the  acids  in  the 
soil  (carbonic  acid,  humus  acids,  etc.)  render  this 
"fixed"  food  soluble  and  available  to  the  plant.  The 
air  which  circulates  in  the  soil  is  of  immense  import- 
ance in  promoting  chemical  processes  which  prepare  and 
set  free  plant-food  of  all  kinds  and  especially  nitrogen 
compounds  (see  pages  148  and  383) .  Where  the  air  sup- 


146  EXPERIMENTS    WITH  PLANTS 

ply  is  deficient,  tlie  soil  becomes  sour  by  the  accumu- 
lation of  carbon  dioxide  and  humous  acids  and  the  roots 
are  killed;  at  the  same  time  poisonous  substances  are 
formed  which,  if  air  were  present,  w^ould  be  converted 
into  plant-food.  Subsoils,  when  exposed  to  air,  usually 
change  color,  an  indication  of  chemical  action. 

The  soil  is  not  only  a  sponge,  from  ivJiich  the  plant 
may  obtain  tvater,  but  also  a  storeJiouse  of  plant -food, 
and  a  laboratory  in  which  plant-food  is  prepared  and 
dissolved  for  the  use  of  the  plant. 

The  amount  of  food  in  the  soil  depends  partly  on 
the  kind  of  rock  from  which  it  is  derived,  partly  on  its 
"fixing"  power,  and  partly  on  the  kind  and  quantity 
of  plants  which  grow  upon  it.  In  all  these  respects 
clay  is  superior  to  sand^;  the  rocks  from  which  it 
comes  are  richer  in  food  than  the  quartz  from  which 
sand  is  formed:  it  has  greater  "fixing"  power  than 
sand^  and  produces  a  greater  growth  of  plants  whose 
decay  enriches  it  still  further:  decay  proceeds  more 
slowly  in  clay  than  in  sandy  soils  (since  it  is  colder 
and  wetter),  and  the  products  of  decomposition  are 
more  fully  fixed  by  it.  For  these  reasons  (and  also 
because  they  contain  more  water)  clay  soils  are  richer 
in  plant- food  than  sandy ^  soils.  The  best  soil  is  a 
mixture  of  sand,  clay  and  humus,  which  gives  abun- 
dant food  and  good  tilth. 

1  The  so-called  "sand"  of  arid  regions  is  as  rich  or  richer  than  clay,  since 
it  comes  from  rocks  rich  Jn  plant-food  and  is  not  leached  by  frequent  rains. 


THE    WOBK   OF   BOOTS  147 

Even  the  best  soil  becomes  exhausted  of  certam 
elements  in  time  if  crops  are  continuously  removed 
from  it.  The  deficient  food  elements  must  then  be  re- 
placed by  fertilizers.  The  chief  substances  which  it  is 
necessary  to  replace  in  this  way  are  nitrogen,  phos- 
phoric acid,  lime  and  potash.  It  is  important  to 
understand  how  best  to  supply  these  elements,  since 
this  knowledge  often  makes  all  the  difference  between 
successful  and  unsuccessful  farming. 

How  may  nitrogen  be  supplied  to  the  soil  ?  Manure 
piles  smell  strongly  of  ammonia  gas  (which  contains 
over  80  per  cent  nitrogen),  and  manure  is  the  most 
available  source  of  nitrogen  as  fertilizer.  In  fresh  ma- 
nure the  nitrogen  is  mostly  insoluble,  but  on  stand- 
ing it  decomposes  (by  the  action  of  bacteria,  see  page 
383)  into  soluble  substances  containing  nitrogen  and 
into  ammonia  gas  and  nitrogen  gas.  These  gases  will 
mostly  escape  into  the  air  and  be  lost  unless  we  mix 
soil  with  the  manure  so  as  to  form  compost:  the  soil 
absorbs  the  ammonia  gas  to  a  marked  extent  and  it  is 
then  changed  to  soluble  compounds  of  nitrogen.^     Air 

'  The  absorption  of  ammonia  gas  by  soil  may  be  shown  by  filling  a  test- 
tube  with  mercury,  closing  with  the  finger  and  inverting  in  a  dish  of  mercury 
so  that  it  contains  no  air:  now  introduce  ammonia  gas  by  heating  ammonia 
water  in  a  flask,  through  the  cork  of  which  passes  a  tube  to  conduct  the  gas 
into  the  test-tube  (heat  at  first  long  enousrh  to  drive  out  air);  when  the  test- 
tube  is  full  of  gas,  introduce  a  lump  of  dry  clay  from  below:  it  will  absorb  the 
gas  and  the  mercury  will  rise.  In  a  control  experiment  use  sand.  Cottonseed 
oil  may  be  used  in  place  of  mercury  by  wedging  a  lump  of  clay  in  the  top  of 
an  ordinary  tube,  dipping  the  tube  into  a  vessel  of  oil  and  then  corking  it  at 
the  top  with  a  rubber  cork  in  such  a  manner  that  the  oil  fills  the  tube  nearly 
to  the  clay.  Raise  the  tube  and  introdtice  the  gas  as  before.  In  each  case 
use  a  control  tube  containing  no  soil.  Decomposing  humus  also  absorbs  a 
good  deal  of  ammonia  gas. 


148  EXPERIMENTS    WITH   PLANTS 

hastens  decomposition,  and  if  it  is  admitted  too  freely 
into  the  compost  heap  the  gases  will  form  more  rap- 
idly than  they  can  be  absorbed:  if,  on  the  other  hand, 
air  is  excluded,  decomposition  almost  stops.  Hence 
decomposition  may  be  regulated  by  regulating  the 
moisture  and  compactness  of  the  heap.  Since  manure 
contains  all  the  mineral  constituents  needed  by  the 
plant,  it  is  by  far  the  best  fertilizer  for  general 
purposes. 

Another  source  of  nitrogen  is  decomposing  plants, 
such  as  leaf- mold,  peat,  etc.  This  is  known  as 
humus.  It  contains  less  soluble  nitrogen  than  manure 
and  decomposes  more  slowly.  The  humus  in  decom- 
posing forms  ammonia  and  sets  free  acids  which  pro- 
mote the  formation  of  soluble  plant-food:  these  acids 
often  change  the  color  of  the  soil  where  it  is  in  imme- 
diate contact  with  dead  roots,  etc.  Humus  may  be  ap- 
plied to  the  soil  by  plowing  in  straw,  stubble,  weeds  or 
special  crops  grown  for  the  purpose. 

Rapidly  acting  nitrogenous  manures  are  urine, 
guano  (manure  of  sea-birds),  saltpeter  and  Chili  salt- 
peter, all  of  which  contain  large  amounts  of  nitrogen 
in  soluble  form.  They  are  especially  valuable  as 
"forcing"  manures  and  to  tide  a  crop  over  a  critical 
period. 

Experiments  have  shown  that  not  more  than  one- 
half  to  one-third  of  the  nitrogen  applied  as  manure  is 
recovered  in  the  crop:   the  waste  is  due  partly  to  the 

lilBBABT  OF 
N.  C.  STATB  C0LI>B€H5 


TH£J    WORK   OF   ROOTS 


149 


escape  of  ammonia  and  nitrogen  gas  and  partly  to 
the  rain,  which  washes  the  soluble  nitrogen  compounds 
out  of  the  soil. 

Some   plants   have    the   power    of   taking   nitrogen 


1 

% 

^  •  -Y 

m 

1 

i"^ 

¥ 

i 

m 

7 

V 

M 

i 

"7~TM 

M 

\I/J 

^y 

98.    Tubercles  on  roots  of  Clover, 

from  the  air  by  means  of  the  bacteria  or  minute  plants 
which  inhabit  tubercles  on  the  roots.  Such  plants 
are  Clover  (Fig.  98),  Lupines,  Beans  and  other  mem- 
bers of  the  Pea  family.  A  crop  of  Clover  or  Lupines 
plowed  under  and  allowed  to  decay  furnishes  nitrogen 


150  EXPERIMENTS    WITH   PLANTS 

to  the  soil:  such  crops  are  called  green  manures  (see 
page  384). 

Certain  other  bacteria  living  free  in  the  soil  take 
nitrogen  from  the  air  and  render  it  available  to  plants, 
while  still  others  act  on  the  humus  and  set  free  nitro- 
gen in  soluble  form  (see  pages  383  and  384) . 

Most  forest  trees  have  their  roots  covered  with 
fungi  (small  colorless  plants),  which  absorb  and  de- 
compose the  humus  in  which  such  trees  grow  and 
render  it  available  to  the  roots. 

How  may  phosphorus  be  supplied  to  the  soil  ?  Phos- 
phorus as  fertilizer  is  chiefly  obtained  from  bones. 
If  we  soak  a  bone  in  muriatic  acid  it  retains  its  form 
but  becomes  like  gristle,  because  the  mineral  con- 
stituents are  dissolved  out:  if,  on  the  other  hand,  we 
burn  it,  it  also  retains  its  form  but  becomes  brittle 
because  the  gristly  substance  has  been  burned  away, 
leaving  the  earthy  constituents,  which  consist  of  phos- 
phoric acid  and  lime.  The  burned  bone  may  now  be 
pulverized  and  spread  on  the  land  as  fertilizer,  where 
it  is  so  very  slowly  dissolved  by  the  carbonic,  humous 
and  other  acids  in  the  soil- water  as  to  be  scarcely 
at  all  available  for  absorption  by  the  roots.  By 
treating  bone  with  sulphuric  acid,  we  obtain  what  are 
known  as  superphosphates,  which  dissolve  readily 
in  water:  when  placed  in  the  soil  the  superphosphates 
are  changed  back  into  the  ordinary  "insoluble"  phos- 
phates, but  they  are  divided  into  very  fine  particles 


THE    WORK   OF   ROOTS  151 

and  distributed  just  where  the  roots  can  get  at  them 
instead  of  being  in  coarse  particles  on  the  surface, 
as  is  the  case  with  ground  bone,  burnt  bone,  etc. 
Consequently  the  superphosphates  give  far  better 
results  than  ordinary  ground  bone. 

Bone  meal  is  usually  ground  bone,  steamed  to 
render  it  more  soluble.  It  contains  both  the  earthy 
and  the  gristly  constituents  (the  latter  contain  nitro- 
gen), but  on  account  of  its  greasiness  decomposes 
slowly  and  dissolves  very  little.  Bone-black  is  burnt 
bone;  it  contains  practically  no  nitrogen.  Certain 
kinds  of  slag  and  rocks  rich  in  phosphoric  acid  are 
also  used  as  fertilizers. 

How  may  lime  be  supplied  to  the  soil  ?  Aside  from 
the  bones,  we  have  as  sources  of  lime,  marl,  marble, 
shells,  land -plaster^  (also  called  plaster  of  Paris,  gyp- 
sum and  sulphate  of  lime),  limy  soils,  etc.  Lime  acts 
much  more  quickly  if  burnt,  since  it  then  dissolves  in 
water,  while  if  air- slaked  it  is  more  slowly  dissolved 
by  the  acids  in  the  soil -water.  The  amount  of  lime 
in  the  soil  can  be  judged  by  the  condition  of  the  well- 
or  spring- water.  If  this  contains  much  lime  it  is 
"hard"  and  deposits  a  scale  (composed  principally  of 
lime)  on  the  in  sides  of  tea-kettles,  boilers,  etc.  It 
may  be  softened  for  cooking  purposes  by  boiling,  or 
for  washing  purposes  by  adding  soda  (or  other  alkali). 

^A  story  is  told  of  Ben.i.  Franklin,  that  he  strewed  fjypsum  on  a  Clover  field 
in  such  away  that  the  words  "This  has  been  plastered"  appeared  conspicuonsly, 
owing  to  the  more  luxuriant  growth  where  the  gypsum  was  applied. 


152  EXPERIMENTS    WITH  PLANTS 

It  may  also  be  softened  by  adding  more  lime  (about 
one  pint  of  lime-water  to  ten  pints  of  hard  water). 
Waters  which  readily  redden  litmus  contain  much  lime. 

In  addition  to  being  itself  a  food,  lime  sets  free 
potash  in  soluble  condition  from  the  insoluble  com- 
pounds in  which  it  is  held,  and  increases  the  power  of 
the  soil  to  "fix"  potash  and  phosphoric  acid;  lime 
greatly  hastens  the  decomposition  of  humus  and  ma- 
nure, sweetens  the  sour  soil  by  combinhig  wdth  acids 
and  destroys  many  injurious  insects  and  fungi.  It 
improves  the  texture  of  the  soil  by  flocculating  clay. 
This  may  easily  be  shown  by  rubbing  up  clay  in  water 
and  adding  a  little  of  this  turbid  water  to  lime-water 
(use  distilled  or  rain-water  as  a  control) .  We  may  also 
mix  burnt  lime  with  clay  and  observe  the  effect  on  the 
mass  when  it  hardens. 

How  may  potash  be  supplied  to  the  soil  ?  Wood  ashes 
contain  large  quantities  of  potash  and  constitute  the 
best  potash  fertilizers.  "Muriate"  of  potash  (potas- 
sium chloride)  and  sulphate  of  potash  are  also  used. 
Gypsum  and  lime  set  free  soluble  potash  in  the  soil 
from  insoluble  compounds,  as  does  also  common  salt. 
Crops  may  be,  therefore,  supplied  with  potash  by  ap- 
plying lime  or  gypsum  to  the  soil,  where  the  soil  con- 
tains sufficient  insoluble  potash. 

Fertilizers  which  dissolve  quickly  when  applied  to 
the  soil  are  much  superior  to  those  which  decompose 
slowly   (unless  the  cost  is  too  great),  since  they  give 


THE   WOBK  OF  ROOTS  153 

immediate  results:  the  use  of  such  fertilizers  (e.  g., 
guano  and  superphosphates)  has  revolutionized  agri- 
culture and  made  high  farming  and  intensive  farming 
possible.  For  example,  we  now  use  from  100  to  200 
pounds  of  superphosphates  per  acre  where  a  hundred 
years  ago  1,000  to  2,000  pounds  of  bone  were  used; 
i.  e.,  for  the  same  cost  it  is  now  possible  to  fertilize 
six  to  eight  times  as  much  land. 

When  the  soil  is  deficient  in  one  constituent  only,  a 
small  amount  of  fertilizer  containing  this  constituent 
will  give  results  out  of  all  proportion  to  its  cost.^ 
Hence  it  is  important  to  know  what  elements  of  plant- 
food  are  lacking  in  the  soil  before  attempting  to  enrich 
it.  Chemical  tests  are  useful,  but  in  most  cases  the 
question  is  practically  settled  by  applying  fertilizers 
and  noting  the  result.  For  the  soil  of  our  particular 
region  we  may  arrange  an  experiment  as  follows:  Lay 
out  beds  wherever  convenient,  or  bring  in  the  soil  and 
place  it  in  pots.  On  each  bed  or  in  each  flower -pot 
place  a  single  fertilizer  or  combination.  We  may  use 
whatever  is  obtainable.     A  good  series  is 

General  fertilizers:  Special  fertilizers: 

{a)  Well-rotted  stable  manure  (6)  Chili  saltpeter 

(c)    Superphosphates 
{d)  Wood  ashes 
(e)   Quicklime 

^See  Bailey:  "Principles  of  Agrriculture,"  Chapters  V  and  VI;  King:  "The 
Soil,"  Cliapter  III;  Roberts:  "Fertility  of  the  Land";  also  articles  in  the  Year- 
Book  of  the  U.  S.  Dept.  of  Aericulture,  for  1894  by  Wiley  and  Webber;  for 
1895  by  Snyder;  for  1896  by  Wiley;  for  1898  by  Means;  for  1899  by  Wiley;  for 
1901  by  Woods;  for  1902  by  Holmes,  Woods  and  McKenney. 


Lbs.  per  square 

yard, 

.  1 

to 

IX 

•     A 

to 

A- 

2  4 

to 

-A- 

.       % 

to 

X 

.1% 

to  4 

154  EXPElilAMt:NTS    WITH   PLANTS 

Lay  out  six  beds  a  yard  square;^  in  each  bed  place 
a  different  fertilizer,  working  it  well  into  the  soil 
with  a  spade.  The  amount  to  be  used  may  be  deter- 
mined by  finding  the  amount  used  per  acre  in  practice 
and  dividing  this  by  4,840  (the  number  of  square  yards 
per  acre).  The  following  will  give  an  approximate 
idea  of  these  amounts: 

Lbs.  per  acre. 
{a)  Stable  manure    ....  5,000  ta    8,000 
(&)  Chili  saltpeter    ....      200  to        300 

(c)  Superphosphate  ....      200  to        300 

(d)  Wood  ashes 1,500  to     2,500 

(e)  Quicklime 8,000  to  20,000 

The  wood  ashes  used  should  be  unleached  ashes 
from  cordwood  (i.  e.,  ordinary  wood-stove  ashes),  in 
which  case  they  contain  about  one  pound  of  potashes 
in  twelve  of  ashes:  the  rest  consists  chiefly  of  lime. 
If  we  wish  to  add  potash  without  lime  we  may  use 
commercial  potashes,  saleratus  or  pearl-ash  at  the  rate 
of  one  thirty- sixth  to  one  twenty-fourth  pound  per 
square  yard:  this  should  be  dissolved  in  two  or  three 
gallons  of  water  and  applied  in  liquid  form. 

Inasmuch  as  the  amount  needed  varies  greatly  with 
the  character  of  the. soil,  it  would  be  desirable  to  make 
a  parallel  series  of  three  beds  for  each  kind  of  ferti- 
lizer, using  on  one  only  half  the  amount  given  above, 
on  another  the  given  amount,  and  on  the  third  half  as 
much  again  as  the  given  amount.    In  case  there  seems 

1  These  .should  be  separated  from  each  other  by  an  interval  of  several  feel, 
to  prevent  the  applied  fertilizer  from  diffusing  from  one  plot  to  another. 


77//;  woinc  OF  HOOTS  155 

to  be  an  injurious  effect  due  to  too  mucli  fertilizer,  try 
the  effect  of  giving  it  in  two  or  three  applications  a 
few  weeks  apart. 

In  each  bed  should  be  sown  Wheat  or  some  staple 
crop;  the  watering  and  other  conditions  should  be 
alike  for  all  the  beds.  The  result  is,  of  course,  strictly 
valid  only  for  the  special  soil  and  special  kind  of  crop 
used,  but  if  the  soil  be  typical  of  the  region  and  the 
crop  a  staple  there  the  result  will  be  of  great  value. 
Moreover,  it  will  also  have  important  general  appli- 
cations. 

The  following  rapid  method  of  soil-testing,  used  by  Prof.  R.  H. 
Loughridge,  of  the  California  Experiment  Station,  enables  one  to  make 
a  test  in  half  an  hour  which  is  sufficient  for  all  practical  purposes.^ 

Nitrogen  and  Humus. —  To  1  part  (by  volume)  of  soil  add  5  parts 
(by  volume)  of  10  per  cent  caustic  potash;  this  is  best  done  in  a  test- 
tube.  Heat  to  boiling  point  and  then  set  aside  for  five  to  ten  minutes. 
If  the  liquid  is  black  and  opaque,  it  indicates  abundant  humus  and  nitro- 
gen: if  the  liquid  allows  light  to  pass  through  when  held  up  at  a 
window,  the  humus  and  nitrogen  content  is  low;  if  the  liquid  is  merely 
yellow,  the  content  of  these  substances  is  very  low.  The  test  really  tells 
us  about  the  humus  only,  but,  since  in  all  except  very  arid  regions  the 
humus  content  is  an  accurate  index  of  the  nitrogen  content,  the  test  is 
of  great  value.  Try  this  test  on  a  soil  rich  in  humus,  such  as  leaf-mold 
or  soil  from  a  grove  or  forest;  also  on  some  sandy  soil  containing  little 
humus.  The  color  of  the  soil  is  a  good  indicator  of  the  amount  of  humus 
it  contains;  the  blacker  it  is  the  more  humus  in  it. 

Phosphorus. —  First  prepare  a  standard  of  comparison  as  follows: 
Take  about  a  pint  of  sand  (as  pure  as  possible)  and  pour  on  it  about 
three  times  its  volume  of  dilute  hydrochloric  acid,  made  in  the  propor- 
tion of  one  part  of  acid  to  four  of  water.     Allow  this  to   stand  for  an 

^The  necessary  reagents  are  obtainable  at  drug  stores. 


156  EXPERIMENTS    WITH   PLANTS 

hour  or  so,  stirring  it  up  from  time  to  time.  Next  place  it  in  the  sink 
and  allow  water  to  run  through  it  for  some  time,  until  water,  after  being 
thoroughly  stirred  up  with  it,  no  longer  gives  any  acid  reaction  to  litmus. 
Spread  the  sand  out  to  dry  and  when  fairly  dry  take  25  grams  for  the 
experiment,  setting  the  rest  aside  for  subsequent  tests.  The  sand  thus 
treated  has  all  the  soluble  plant- food  washed  out.  We  will  now  proceed 
to  add  to  it  definite  amounts  of  plant-food  in  order  that  we  may  see  what 
results  these  amounts  give  in  our  tests.  A  good  conient  of  soluble^ 
phosphoric  acid  in  the  soil  is  one-tenth  of  one  per  cent.  We  will  there- 
fore add  this  amount  to  the  sand  and  make  a  test.  To  the  25  grams  of 
sand  add  5  cc.  of  %  per  cent  phosphoric  acid  (made  by  dissolving  one 
gram  of  solid  phosphoric  acid  in  200  ec.  of  water)  :  this  will  give  .025 
gram  in  25  grams  of  sand,  or  one-tenth  of  one  per  cent.  Take  two  grams 
of  the  sand  which  has  been  moistened  with  the  acid,  burn  it  for  five 
minutes  on  a  red-hot  shovel:^  place  it  in  a  test-tube  and  add  3  or  4  cc. 
of  pure  nitric  acid;  heat  until  it  just  begins  to  boil;  add  2  or  3  cc.  of 
water  and  filter.  Allow  4  or  5  cc.  of  water  to  lun  through  the  sand  into 
the  filtered  liquid,  in  order  to  wash  out  the  acid,  and  add  to  the  filtered 
liquid  an  equal  volume  of  a  solution  of  molybdate  of  ammonia.  (This  is 
made  by  adding  10  grams  of  ammonium  molybdate  to  25  cc.  of  distilled 
water;  then  add  15  cc.  of  strong  ammonia  (chemically  pure)  and  150 
grams  nitric  acid  (chemically  pure):  keep  warm  and  if  a  yellow  precipi- 
tate occurs  pour  oflf  the  clear  liquid  for  use.)  Warm  until  it  feels  rather 
hot  to  the  hand,  then  put  it  aside  to  settle.  Pour  off  the  clear  liquid  at 
the  top  and  transfer  the  rest  to  a  small  funnel,^  the  neck  of  which  is  not 
more  than  one-twelfth  of  an  inch  in  diameter  inside  and  whi<?h  is  sealed 
tightly  at  the  bottom  with  sealing-wax.  On  the  outside  of  the  neck 
paste  a  paper  scale  ruled  in  millimeters  (or  in  tenths  of  an  inch).     Let 

1  That  is,  soluble  in  the  acids  which  are  ordinarily  used  in  making  tests:  the 
soil  may  contain  a  great  deal  more  phosphoric  acid  in  insoluble  form,  but  this 
will  not  appear  in  the  tests  and,  being  insoluble,  is  not  directlj'  available  to  the 
plant. 

2  The  burning  is  for  the  purpose  of  removing  vegetable  matter  and  humus, 
and  should,  with  ordinary  soil  samples,  be  carried  on  until  the  soil  is  light 
gray  in  color. 

3  Still  better  are  the  tubes  used  vtith  centrifugal  apparatus. 


THE    WORK   OF   BOOTS  157 

us  suppose  that  the  precipitate'  when  it  has  all  settled  in  the  neck  of  the 
funnel  forms  a  column  one  millimeter  high.  We  know  that  this  indi- 
cates a  content  of  one-tenth  of  one  per  cent  of  phosphorus  in  the  soil 
examined.  If  we  now  examine  soil  from  the  garden  in  the  same  way  and 
find  only  one-half  a  millimeter  of  precipitate  (using  the  same  funnel),  it 
indicates  only  one-twentieth  of  one  percent,  which  is  poor.  Such  a  soil 
will  be  benefited  by  the  application  of  phosphoric  acid  in  some  of  the 
forms  previously  described. 

Lime, —  We  usually  know  whether  a  soil  contains  much  lime  by  the 
hardness  of  the  water  and  the  amount  of  scale  it  deposits  on  tea  kettles 
and  boilers.  If  a  drop  of  strong  hydrochloric  acid  produces  efiEervescence 
(i.  e.,  an  appearance  of  bubbles  of  gas)  when  placed  on  a  sample  of  soil, 
it  indicates  the  presence  of  an  excess  of  lime.  Take  25  grams  of  the 
sand  which  has  been  treated  with  dilute  hydrochloric  acid  as  described 
above,  and  add  to  it  a  quarter  of  a  gram  of  whiting  or  marble  dust, 
which  will  give  us  a  content  of  one  per  cent  of  carbonate  of  lime  in  the 
soil:  this  should  be  thoroughly  and  equally  mixed  throughout  the  entire 
mass  of  sand.  Place  5  grams  of  this  sand  in  a  test-tube;  add  4  or  5  cc. 
of  hydrochloric  acid  (chemically  pure) ;  heat  until  it  just  begins  to  boil ; 
add  strong  ammonia  water  (chemically  pure)  until  the  liquid  smells  of 
ammonia;  filter  while  hot  and  add  5  cc.  of  a  saturated  solution  of  oxa- 
late of  ammonia  (made  by  filling  a  bottle  about  one-fourth  full  of 
oxalate  of  ammonia,  then  filling  with  water  and  allowing  it  to  stand  until 
saturated).  Transfer  to  the  funnel  just  described  and  allow  the  precipi- 
tate^ to  settle.  If  the  column  of  precipitate  is  two  millimeters  long  we 
know  that  a  sample  of  soil  treated  in  the  same  way  which  gives  a  column 
of  precipitate  one  millimeter  long  indicates  only  one-half  as  much  lime, 
or  %  per  cent,  etc.  In  a  sandy  soil  1  to  2  per  cent  of  lime  is  about  right; 
in  a  clay  soil  three-tenths  to  five-tenths  of  one  per  cent  is  good;  10  to  15 
per  cent  is  an  excess  in  any  soil. 

Alkali. —  To  20  grams  of  the  sand  which  has  been  treated  with  dilute 
hydrochloric  acid  add  4  cc.  of  a  solution  made  by  dissolving  in  100  cc. 
of  water  1  gram  sodium  carbonate'  (washing  soda),  1  gram  sodium  chlo- 

1  The  precipitate  is  molj'bdo-phosphate  of  ammonium. 

2  The  precipitate  is  oxalate  of  lime. 

^Allowance  has  been  made  for  water  of  crystallization. 


158  EXPERIMENTS    WITH   PLANTS 

ride  (eoimuoa  salt)  and  3.3  grams  sodium  sulphate^  (Glauber's  salt). 
This  gives  a  content  in  the  soil  of  one-tenth  of  one  per  cent  soda,  two- 
tenths  of  one  per  cent  common  salt  and  three-tenths  of  one  per  cent 
Glauber's  salt:  these  are  all  excessive  and  hurtful  amounts,  and  a  soil 
which  contains  so  much  of  either  is  not  suitable  for  ordinary  crops. 
Place  filter  paper  in  a  funnel  and  put  the  soil  in  it;  add  20  cc.  of  water 
and  let  it  leach  through  into  a  test-tube;  test  with  litmus  paper.  The 
rapidity  with  which  the  paper  turns  blue  indicates  the  amount  of  black 
alkali  or  sodium  carbonate:  if  it  quickly  turns  deep  blue  it  indicates  an 
excessive  amount  (one-tenth  of  one  per  cent  or  more:  if  it  turns  blue 
very  slowly  it  indicates  a  lesser  amount).  Dilute  some  of  the  filtered 
liquid  with  one,  two  and  three  volumes  of  water  and  test  with  litmus 
paper.  Save  some  of  the  filtered  liquid  to  be  used  as  a  standard  of  com- 
parison on  future  occasions.  Take  a  portion  of  the  filtrate  and  test  for 
common  salt  as  follows:  Add  a  few  drops  of  nitric  acid  (chemically  pure) 
and  then  a  drop  or  two  of  a  1.7  per  cent  solution  of  nitrate  of  silver 
(this  is  made  by  adding  1.7  grams  to  100  cc.  of  water);  a  curdy  pre- 
cipitate^ shows  an  excessive  amount  of  salt  (two  tenths  of  one  per  cent 
or  more)  and  from  this  we  may  find,  in  testing  soils,  all  amounts  down 
to  a  trace  which  gives  only  a  slight  milkiness  on  the  addition  of  nitrate 
of  silver.  Take  another  portion  of  the  filtered  liquid,  and  test  for 
Glauber's  salt,  as  follows:  add  a  few  drops  of  hydrochloric  acid  (chemi- 
cally pure),  heat  and  add  a  few  drops  of  barium  chloride  to  the  hot 
solution:  transfer  to  the  funnel  described  above  and  measure  the  amount 
of  precipitate:^  this  will  of  course  indicate  in  the  present  case  a  content 
in  the  soil  of  three- tenths  of  one  per  cent,  which  is  an  excessive  and 
injurious  amount. 

By  these  simple  tests  which,  although  only  rough  approximations, 
nevertheless  serve  admirably  for  practical  purposes,  we  may,  after  our 
standards  of  comparison  are  once  established,  in  a  few  moments  learn 
whether  a  given  soil  is  deficient  in  any  of  the  important  elements  of 
plant-food  and  whether  it  contains  injurious  amounts  of  alkali. 

1  Allowance  has  been  made  for  water  of  crystalization. 

2  The  precipitate  is  silver  chloride. 
^The  precipitate  is  barium  suli)hate. 


THE    Wo/i'h'   OF   BOOTS  159 

Alkali  Soils. —  The  tests  for  alkali  are  of  importance  in  arid  and 
semi-arid  regions.  Wlienever  the  ra  nfall  is  small  tlie  salts  are  not 
leached  out  of  the  soil  so  fast  as  they  are  formed  and  they  accumulate. 
As  the  rainwater  evaporates  they  are  left  on  the  surface  ( see  experiment 
on  page  127),  where  they  often  form  a  whitish  deposit  which  disappears 
during  a  rain  but  reappears  as  soon  as  the  soil  begins  to  dry  out.  These 
salts  may  be  in  the  form  of  "black  alkali,"  or  sodium  carbonate  (so  called 
because  it  combines  with  the  humus  to  form  a  black  mass);  such  "black 
alkali"  spots  are  very  conspicuous.  This  is  the  worst  form  of  alkali,  for 
it  corrodes  the  plant  just  at  the  surface  of  the  soil  and  kills  it.  By  adding 
gypsum  (sulphate  of  lime)  the  "black  alkali"  is  changed  to  "white 
alkali,"  Glauber's  salt  (sodium  sulphate)  and  carbonate  of  lime.  Glau- 
ber's salt,  together  with  common  salt  (sodium  chloride),  magnesium  salts, 
etc.,  are  called  "white  alkali":  they  are  much  less  injurious  than  "black 
alkali."  Quantities  of  alkali  salts  are  often  found  at  varying  distances 
(down  to  several  feet)  below  the  surface  of  the  soil,  where  they  form 
compact  masses  known  as  alkali  hardpan  ;  its  presence  may  be  ascertained 
(like  that  of  any  hardpan)  by  sounding  the  soil  with  a  sharp-pointed 
steel  rod  to  the  depth  of  four  or  five  feet  at  least  or  by  digging  holes. 
When  we  begin  to  irrigate  such  land  the  alkali  of  the  hardpan  often 
rises  and  the  alkali  spots  on  the  surface  gradually  become  larger 
and  larger.  The  experiment  already  described  on  page  127  shows 
clearly  how  this  takes  jilace  ;  in  this  case  the  salt  in  the  bottom  of  the 
tumbler  represents  the  alkali  hardpan.  This  rise  does  not  take  place  if 
the  irrigation  is  properly  done  ;  only  excessive  application  of  water 
brings  it  about.  This  suggests  that  we  might  reverse  the  operation  by 
flooding  the  land  with  water  and  carrying  it  otf  by  means  of  drains  placed 
underground.  This  would  correspond  to  placing  the  tumbler  of  sand  used 
in  the  experiment  under  the  faucet  and  allowing  the  water  to  run  out  of 
a  crack  in  the  bottom  ;  it  is  very  evident  that  the  salt  would  soon  dis- 
appear. Large  areas  of  alkali  lands  have  been  reclaimed  in  this  way, 
which  furnishes  the  only  practical  method  of  reclamation.  To  wash  out 
the  salts  completely  would  be  a  disadvantage,  since  they  consist,  to  a 
considerable  extent,  of  substances  needed  by  the  plant.  The  water  of 
moderately  alkaline  lakes  can  be  used  for  reclaiming  alkali  soils,  if  enough 


160  EXPEEIMENTS    WITH   PLANTS 

be  used  to  wash  down  through  the  soil  and  out  through  the  drains. 
But,  if  only  a  little  be  used,  it  remains  in  the  soil  and  finally  evaporates 
at  the  surface,  thus  adding  its  dissolved  salts  to  the  alkali  already  present 
in  the  soil.^  In  addition  to  the  injurious  effects  mentioned  above,  the 
alkali  salts  (especially  the  black  alkali)  destroy  the  tilth  and  keep  the 
soil  in  a  permanently  paddled  condition;  this  is  noticeable  at  the  surface, 
where  a  thick,  hard  crust  forms  on  alkali  lands. 

Each  kind  of  crop  needs  a  somewhat  different  food 
from  any  other  kind.  A  cereal  crop  takes  from  the 
soil  only  one -half  as  much  nitrogen  and  about  one- 
fourth  as  much  potash  as  root  crops.  Clover  will  grow 
where  Wheat  cannot  and  will  leave  the  land  fit  for 
Wheat  again.  This  is  partly  on  account  of  its  deep 
roots,  which  take  food  from  a  considerable  depth  and 
raise  it  to  the  surface,  partly  on  account  of  its  power 
of  taking  nitrogen  from  the  air  and  partly  because  the 
roots  and  stubble,  etc.,    improve  the  tilth  of  the  land. 

In  practice,  crops  with  similar  needs  are  not  raised 
in  succession  on  the  same  land:  deep-rooted  crops  al- 
ternate with  shallow-rooted,  etc. :  white  crops  (cereals) 
are  usually  alternated  with  green  crops  (Clover,  etc.). 
This  alternation  is  known  as  the  rotation  of  crops. 
Find  out  as  much  as  you  can  about  the  rotation  of 
crops  in  actual  practice.^ 

From  what  has  just   been  said,  it  is  evident  that 

1  See  Hilgard  ;  "Origin,  Value  and  Reclamation  of  Alkali  Lands  ;  "  Year- 
Book  of  the  Dept.  of  Agriculture,  1895.  Also  the  following  bulletins  of  the  Cali- 
fornia Experiment  Station  :  Bulletin  No.  133,  R.  Loughridge,  "Tolerance  of 
Alkali  by  Various  Cultures";  Bulletin  128,  Hilgard,  "Nature,  Value  and  Utiliza- 
tion of  Alkali  Lands." 

2  Rotation  of  crops  also  tends  to  destroy  weeds,  fungi,  insect  pests,  etc. 


THE   WORK   OF  BOOTS  161 

each  plant  selects  from  the  soil  certain  elements  which 
it  absorbs  and  uses  for  its  growth,  to  the  partial  or 
total  exclusion  of  others.  Thus,  when  we  grow  plants 
in  a  solution  of  Chili  saltpeter  (sodium  nitrate)  the 
plant  takes  up  all  the  nitrogen  and  only  a  trace  of  the 
sodium,  leaving  the  rest  in  solution.  From  ammonium 
sulphate  the  plant  takes  the  ammonia,  leaving  most  of 
the  sulphuric  acid. 

This  selective  action  depends  on  the  fact  that  more 
nitrogen  is  used  or  combined  within  the  plant  than 
sodium.  This  action  of  the  plant  may  be  imitated 
artificially  by  closing  the  end  of  a  tube  or  lamp-chimney 
with  a  piece  of  bladder,  as  described  on  page  60,  plac- 
ing within  it  water  and  a  few  pieces  of  zinc  and  setting 
it  in  a  glass  containing  a  solution  of  copper  sulphate 
(blue  stone)  in  water.  The  copper  sulphate  diffuses 
through  the  membrane  and  the  copper  is  deposited  on 
the  metal  and  so  removed  from  the  solution,  while 
the  sulphuric  acid  is  left  behind:  another  substance, 
e.g.,  eosin  in  solution,  will  not  be  taken  up  by  the  ziiic 
but  will  be  taken  up  by  the  membrane,  which  becomes 
strongly  colored:  another  substance,  e.  g.,  common 
salt,  will  not  be  taken  up  by  either  glass,  membrane 
or  metal,  but  will  remain  in  solution  in  its  original 
strength. 

Inasmuch  as  the  root  is  the  most  tender  and  succu- 
lent part  of  the  plant,  it  is  liable  to  attacks  by  insects 
and  animals.    Some  roots,  such  as  Monkshood,  Yellow 


162  EXPERIMENTS    WITH   PLANTS 

Jasmine,  etc.,  are  protected  against  such  attacks  by 
poisonous  substances;  others  by  a  bitter  taste,  such  as 
Chicory,  Dandelion  and  Rhubarb.  Immense  damage 
has  resulted  from  Phylloxera,  an  insect  which  attacks 
the  roots  of  grape-vines  in  Europe.  For  some  reason 
the  roots  of  native  American  grapes  are  not  attacked 
by  the  insect,  and  the  European  varieties  are  therefore 
grafted  upon  them.  It  is  not  known  how  the  roots  of 
American  vines  protect  themselves,  but  the  great  im- 
portance of  such  protection  is  very  evident. 


CHAPTER    IV 


THE   WORK   OF   LEAVES 


We  have  become  familiar  with  the  seed-leaves,  or 
first  leaves  of  the  plant.  We  have  learned  something 
about  their  general  appearance  and  structure;  the 
question  may  now  be  raised,  Of  what  use  are  the  seed- 
leaves?  Remove  the  seed-leaves  from  a  number  of 
plants  (Fig.  99)  about  an  .inch 
high  (growing  in  pots  or  boxes  of 
earth),  and  mark  them  by  loops 
of  colored  twine ;  mark  a  number 
of  uninjured  plants  of  the  same 
size  with  white  twine,  to  serve 
as  controls.  Vary  the  experiment 
by  removing  the  seed  -  leaves 
from  the  soaked  seeds  before 
they  are  planted;  from  some 
remove  one,  from  others  both 
seed-leaves.  Place  them  on  the 
surface  of  moist  earth  in  a  pan, 
and  cover  with  a  glass.  Does 
the  removal  of  the  seed-leaves 
check  the  growth  of  the  plant? 

(103) 


99.  Two  So.uiet  Runner  Beans 
of  the  same  age,  from  one  of 
which  the  seed-leaves  were  re- 
moved shortly  after  germina- 
tion. 


164  EXPERIMENTS    WITH  PLANTS 

Why?  We  notice  that  the  longer  the  seed-leaves  re- 
main on  the  plant  the  more  they  shrivel  and  lose  sub- 
stance. It  looks  as  though  the  plant  were  absorbing 
the  substance  of  the  seed-leaf  to  obtain  food  for  its 
growth. 

Do  the  seed-leaves  contain  food  substances?  The 
principal  food  substances  needed  for  the  growth  of 
plants  and  animals  are  (a)  starches  and  sugars,  (h) 
fats  and  oils,  and  (c)  proteids  (substances  like  white 
of  ^^g).  Let  us  test  the  seed-leaves  to  see  whether 
they  contain  these  substances. 

Test  for  starch  by  means  of  iodine  solution,  made 
by  dissolving  potassium  iodide^  in  water  (about  one 
part  to  seventy-five  of  water),  and  adding  iodine  crys- 
talsMmtilthe  solution  becomes  dark  brown  in  color. 
Apply  the  solution  to  a  freshly  cut  or  broken  surface 
of  the  seed-leaf  (if  the  seed-leaf  is  dry  it  will  take 
the  solution  some  time  to  soak  in).  A  dark  blue  or 
blackish  coloration  indicates  the  presence  of  starch. 

Sugar,  if  present  in  sufficient  quantity,  may  be 
detected  by  taste  (be  careful  not  to  taste  poisonous 
seeds,  e.  g..  Castor-beans) ;  if  none  is  detected  by  this 
means,  use  Fehling's  solution,  which  can  be  made  up 
by  a  druggist. 2  The  seed-leaf  to  be  tested  is  cut  up 
into  thin  slices  and  boiled  for  a  moment  or  two  in  the 

1  Obtainable  at  drug  stores. 

2  This  can  be  made  up  by  any  druggist.  Dissolve  .34.65  grams  of  purified 
copper  sulphate  in  200  cc.  of  water  to  make  Solution  I.  Dissolve  173  grams  of 
sodium   potassium  tartrate    (Rochelle  salt)  in  480   cc.  of  10  per  cent  sodium 


THE    WORK   OF  LEAVES  165 

solution;  a  red  precipitate,  or  sediment,  indicates  the 
presence  of  grape-sugar;  the  precipitate  may  not 
appear  until  the  boiled  solution  has  been  allowed  to 
stand  for  a  time.  (Cane-sugar  may  be  tested  for,  if 
desired,  by  the  methods  described  in  works  on  chem- 
istry; it  is  found  in  seeds  to  such  a  small  extent  that 
it  may  be  neglected.) 

Fats  and  oils,  whenever  abundant,  will  ooze  out 
if  a  pin  is  stuck  into  the  dry  seed-leaf;  a  better 
method  consists  in  powdering  the  substance  of  the  dry 
seed-leaf  (scraping  with  a  knife  usually  suffices  for 
this)  and  placing  it  on  a  piece  of  paper  on  a  clean 
plate  in  a  warm  oven  (not  hot  enough  to  scorch  the 
paper) ;  the  oil,  if  present,  will  make  a  spot  on  the 
paper.  Very  small  quantities  of  oil  may  be  detected 
by  grinding  up  the  seeds  and  extracting  with  benzine 
(or  gasolene,  ether,  chloroform,  etc.);  on  standing, 
the  benzine  will  evaporate,  leaving  the  oil.  Care  must 
be  taken  in  using  benzine  (or  the  other  substances 
mentioned)  not  to  bring  it  near  a  flame  or  stove,  as 
the  vapor  is  highly  inflammable. 

Proteids  may  be  tested  for  by  nitric  acid,  a  drop  of 
which  should  be  placed  on  the  seed-leaf;  it  may  be 
followed  by  a  drop  of  ammonia  to  intensify  the  color. 
A  yellow  color  indicates  the  presence  of  proteid  sub- 
hydrate  (soda  lye)  in  water  to  make  Solution  II.  To  make  up  the  reagent, 
add  to  a  given  quantity  of  Solution  I  two  and  one-half  times  its  volume  of 
Solution  II,  and  one  and  one-half  times  its  volume  of  water.  Make  up  the 
reagent  fresh  whenever  needed. 


166  EXPEBIMENTS    WITH   PLANTS 

stance;  if  the  seed-leaf  is  dry,  time  must  be  allowed 
for  the  acid  to  soak  into  it.  Apply  the  test  to  a  little 
hard-boiled  white  of  egg,. 

Another  very  excellent  test  is  made  by  placing  on 
the  seed-leaf  a  drop  of  a  saturated  solution  of  cane- 
sugar  in  w^ater;  upon  this  place  a  drop  or  two  of 
strong  sulphuric  acid  (chemically  pure) ;  a  bright  red 
color  indicates  the  presence  of  proteids. 

Which  of  the  three  classes  of  substances  seems  to 
be  most  abundant  in  the  seeds  familiar  to  you  ?  Make 
a  table  showing  the  results  of  your  tests,  and  indicate 
by  the  terms  "abundant,"  "little"  or  "none,"  the 
relative  quantity  found. 

In  order  that  the  food  materials  may  reach  the 
places  where  they  are  needed,  they  must  travel  from 
cell  to  cell,  passing  through  the  cell -walls.  To  do  this 
they  must  be  made  soluble.  The  process  of  making 
the  food  soluble  is,  in  a  general  way,  similar  in  animals 
and  plants:  in  animals  it  is  called  digestion;  the  pro- 
cess hi  animals  is  better  understood  than  in  plants  and 
we  may  profitably  study  it  in  both.  In  the  human  body 
it  begins  in  the  mouth,  the  saliva  of  which  contains  a 
chemical  compound  called  diastase,  belonging  to  the 
class  of  bodies  known  as  ferments.  In  order  to  observe 
the  action  of  the  diastase,  boil  a  little  starch  in  water 
to  form  a  paste,  and  place  a  little  of  the  cooled  paste 
on  the  tip  of  the  tongue.  After  a  short  time  it  tastes 
sweet,   indicating  that  some   of  the   starch  has   been 


THJC    WOMK  OF  LEA  VUS  167 

changed  to  sugar  by  the  diastase  (ptyalin)  of  the 
saliva.  Mix  a  little  starch  paste  with  saliva,  warm  it 
to  body  temperature  (by  placing  it  in  a  tube  and  hold- 
ing the  latter  in  the  hand) .  Allow  it  to  stand  at  this 
temperature  for  a  few  minutes;  then  add  Fehling's 
solution  and  boil.  Do  you  get  any  indication  of  grape- 
sugar?  Test  the  starch  paste  and  the  saliva  separately, 
before  mixing,  as  a  control. 

Starch  is  changed  to  grape-sugar  by  uniting  with 
water :  such  union  of  substances  with  water  is  called 
hydrolysis,  and  the  ferments  which  bring  it  about  are 
called  hydrolyzing  ferments.  It  can  be  brought  about 
by  boiling  starch  in  water  for  a  long  time,  or,  in  a 
much  shorter  time,  by  the  addition  of  acid  to  the 
water.  Make  a  very  thin  starch  paste  in  water,  add 
hydrochloric  acid  (a  few  drops  of  acid  to  100  cc.  of 
water;  the  more  acid  used  the  quicker  the  reaction). 
At  intervals  of  about  five  minutes  stir  the  mixture  and 
take  out  two  samples^;  test  one  of  these  (after  cooling) 
by  adding  a  few  drops  of  iodine  solution ;  test  the  other 
by  adding  two  or  three  times  its  own  volume  of  Fehl- 
ing's solution  and  boiling.  At  first  we  get  a  blue 
coloration  with  iodine;  after  boiling  for  a  time,  a 
brownish  color  is  obtained;  still  later  we  find  a  yel- 
lowish coloration. 

The  brown  and  yellowish  colorations  are  due  to  the 

^  If  a  strongly  acid  sohition  is  used,  the  samples  should  be  treated  before 
testing  by  adding  lye  until  they  turn  red  filter  paper  blue. 


168  EXPERIMENTS    WITH  PLANTS 

fact  that  the  starch  is  changed  to  dextrin,  a  substance 
familiar  to  us  in  the  crust  of  bread,  where  it  is  formed 
by  the  action  of  the  heat  on  the  moist  starch  of  the 
flour.  The  characteristic  color  and  taste  of  the  crust 
are  due  t3  the  dextrin,  also  its  stickiness  when  moist- 
ened with  water  (dextrin  is  used  commercially  as 
mucilage).  After  the  acid  solution  has  boiled  for  a 
sufficient  time  the  dextrin  is  all  changed  to  grape- 
sugar,  as  will  appear  upon  testing. 

In  seeds  which  contain  starch  we  may  expect  to 
find  ferments  which  have  the  power  of  hydrolyzing 
starch  and  converting  it  into  soluble  form;  i.  e.,  into 
sugar.  The  most  favorable  seed  for  examination  is 
Barley,  but  any  Grain  will  serve  the  purpose  excel- 
lently. Grind  some  of  the  dry  grain  in  a  mortar  with 
water,  filter,  and  to  the  filtered  liquid  add  twice  its 
volume  of  Fehling's  solution  and  boil.  Allow  it  to 
stand,  and  note  the  amount  of  precipitate.  Do  the 
same  with  some  Barley  which  has  so  far  germinated 
that  the  caulicle  is  about  a  quarter  of  an  inch  long. 
What  difference  in  the  amount  of  precipitate  ?  Has  the 
amount  of  grape-sugar  increased?  Grind  up  some 
more  dry  grain  in  water,  filter,  and  add  to  the  filtered 
liquid  a  little  starch.  After  twenty-four  hours,  test  for 
grape-sugar  with  Fehling's  solution. 

The  first  step  in  the  process  of  brewing  is  to  allow 
Barley  to  germinate  until  the  starch  is  mostly  changed 
to  sugar;  the  grain  is  then  killed  by  heat  and  a  watery 


THE    WOBK   OF  LEAVES  169 

extract  (called  malt)  is  made;  yeast  is  then  added,  by 
the  action  of  which  the  sugar  is  changed  to  alcohol. 

It  is  generally  found  that  seeds  which  contain  starch 
contain  also  diastase,  and  that  during  germination  the 
starch  is  more  or  less  completely  changed  to  sugar  and 
transported  to  the  places  where  it  is  needed.  The  cells 
through  which  it  wanders  usually  contain  starch,  owing 
to  the  fact  that  the  sugar  is  frequently  changed  back 
to  starch  again,  probably  as  often  as  it  reaches  a  cer- 
tain concentration  in  the  cell.  For  this  reason  it  is 
comparatively  easy  to  trace  the  path  from  the  seed- 
leaves  to  the  growing  parts  of  the  plant  by  cutting  the 
plant  into  halves  lengthwise  and  applying  iodine  solu- 
tion to  the  cut  siu'faces.  Trace  the  path  of  the  starch 
in  this  way  in  the  seedlings  you  have  at  your  disposal. 

The  power  of  changing  starch  into  sugar,  which, 
in  human  digestion,  is  begun  in  the  mouth,  is  com- 
pleted in  the  small  intestine,  into  which  the  food 
passes  after  leaving  the  stomach.  The  pancreas  (or 
sweetbread)  pours  into  the  small  intestine  the  pan- 
creatic juice,  containing  different  sorts  of  ferments, 
which  act,  one  on  starch,  another  on  fats  and  others 
on  the  proteids. 

In  order  to  study  the  behavior  of  fats,  take  a  little 
fat  or  oil  in  liquid  form  (melted  butter,  cotton-seed 
oil,  olive  oil  or  cocoanut  oil)  and  mix  it  with  water; 
shake  it  up  in  a  bottle  until  the  mixture  becomes  milky 
in  appearance.    Allow  it  to  stand  and  notice  the  sepa- 


170  i:XPEliIMENTS    WITH  PLANTS 

ration  which  soon  occurs.  Add  a  little  alkali  to  the 
mixture  and  shake  again.  Does  it  separate  as  before  ? 
This  is  called  an  emulsion.  Examine  a  drop  of  it  under 
the  microscope.  Notice  the  very  small  drops  of  fat 
which  float  freely  in  the  liquid.  Compare  the  appearance 
of  milk  under  the  microscope.  The  pancreatic  juice  is 
alkaline  and  has  the  power  of  emulsifying  fats. 

It  also  has  a  further  action,  which  may  be  illus- 
trated by  melting  a  little  cocoanut  oiP  (preferably  on 
a  water-bath)  and  gradually  adding  a  strong  solution 
of  caustic  soda,  stirring  it  in  the  meanwhile.  Very 
soon  a  solid  substance  forms,  whereupon  the  addi- 
tion of  soda  may  be  stopped.  On  dissolving  this 
solid  substance  in  water,  we  recognize  from  the 
feeling,  taste,  odor  and  general  behavior  that  it  is 
soap.  Through  the  action  of  the  alkali  the  oil  has 
been  changed  into  soap  and  glycerine.  A  similar 
reaction  takes  place  in  the  presence  of  the  pancreatic 
juice:  this  reaction  is  due  to  a  ferment  called  lipase 
(steapsin),  which  attacks  fats  in  the  small  intestine 
and  breaks  them  up  into  glycerine  and  fatty  acids- 
which  readily  pass  through  the  cell- walls  and  thus 
become  absorbed. 

Lipase  is  found  in  oil-containing  seeds,  especially 
in  the  Castor-bean.  If  a  few  of  the  Castor- beau s 
(just    sprouting)     be    crushed    and    added    to    fresh 

1  Obtainable  at  drug-stores. 

2  Lipase  also  has  the  power  of  causing  these  substances  to  unite  so  as  to 
form  fats ;  its  action  is  therefore  said  to  be  reversible. 


I 


THE    WORK   OF   LEA  VES  171 

cottonseed  oil  (which  gives  Httle  or  no  acid  reaction 
to  litmus  on  being  shaken  up  with  a  little  alcohol 
and  water)  and  allowed  to  stand  a  few  hours,  the 
oil  will  give  an  acid  reaction,  due  to  the  fact  that 
the  lipase  of  the  Castor-bean  has  split  the  oil  into 
glycerine  and  fatty  acids,  which  latter  react  with  the 
litmus  in  the  presence  of  alcohol  and  water. 

Proteids  are  acted  upon  in  the  animal  body  by 
both  the  gastric  juice  of  the  stomach  and  the  pan- 
creatic juice  of  the  small  intestine.  The  first  con- 
tains a  ferment,  pepsin,  which  acts  only  in  acid 
solutions,  the  second  a  ferment,  trypsin,  which  acts 
only  in  neutral  or  alkaline  solutions. 

Obtain  a  pig's  stomach:  dissect  off  some  of  the 
inner  lining,  cut  it  up  into  small  pieces  with  scissors 
and  pound  it  in  a  mortar  with  water  and  a  little 
glycerine.  Filter  the  fluid, ^  and  add  to  it  pure  strong 
hydrochloric  acid  in  the  proportion  of  1  cc.  of  acid 
to  150  cc.  of  liquid.    In   this  place   a  little  fibrin^  or 

1  Pepsin  (obtainable  at  drug-stores)  may  be  dissolved  in  water  in  the  pro- 
portion of  one-half  i^ram  to  50  cc.  of  water  to  make  artificial  jj:astric  juice.  It 
is  much  better,  howev^er,  to  obtain  a  stomach  for  the  experiment. 

2  Fibrin  may  be  obtained  in  dry  condition  (at  drug-stores),  in  which  case  it 
should  be  softened  by  soaking  in  water,  or  better,  in  water  containing  about  1 
cc.  of  hydrochloric  acid  in  every  100  cc.  Fibrin  may  be  prepared  from  blood 
(obtainable  of  butchers)  by  whipping  it  with  a  bundle  of  sticks  or  wires  :  the 
stringy,  elastic  substance  which  collects  on  them  is  the  fibrin  :  this  is  a  proteid 
substance  (apply  the  test  for  proteids);  wash  it  in  water,  what  is  its  color? 
To  the  fibrin  is  due  the  clotting  of  blood  when  wounds  are  made  :  it  is  very 
quickly  coagulated  by  sugar,  hence  the  value  of  treating  cuts,  etc.,  by  sprink- 
ling them  at  once  with  sugar:  other  substances,  e.  g.,  iron  chloride,  have  a 
similar  action.  If  a  little  blood  be  allowed  to  stand  in  an  open  bottle  the  fibrin, 
together  with  the  red  corpuscles,  collects  into  a  clot,  leaving  a  straw-colored 
liquid  which  occupies  about  half  the  space  :  this  is  the  serum  :  it  is  the  serum 
which  fills  a  blister.  Find  out  what  you  can  regarding  the  composition  of 
blood.     See  any  good  text-book  of  physiology. 


172  EXPERIMENTS    WITH  PLANTS 

some  coagulated  white  of  <dg^^  and  put  in  a  warm 
place.  Keep  as  near  the  body  temperature  as  pos- 
sible. Place  a  little  fibrin  or  white  of  ^^^  in  water, 
also  some  in  acidulated  water  (1  cc.  of  hydrochloric 
acid  in  150  cc.  of  water)  as  controls.  Place  another 
portion  of  coagulated  white  of  ^gg  in  pancreatic 
extract  and  keep  in  the  same  place. 

It  should  be  noted  that  both  the  gastric  and  pan- 
creatic juices  contain  ferments  which  coagulate  the 
proteid  of  milk  (casein) :  this  is  subsequently  rendered 
soluble. 

By  the  action  of  pepsin  and  trypsin  the  proteids 
are  changed  into  soluble  substances  which  can  readily 
be  absorbed  by  the  cells.  It  is  only  natural  to  look 
for  pepsin  and  trypsin  in  seeds.  In  germinating  Corn, 
Barley  and  other  seeds  pepsin  occurs,  while  in  others 
(Pea,  Rye,  Oat)  it  has  not  been  found:  it  is  natural 
to  suppose  that  in  such  cases  other  ferments  take 
its  place.  In  certain  plants  which  capture  and  digest 
insects  (Sundew,  Nepenthes  or  Pitcher  Plant)  occurs 
a  ferment  which  resembles  pepsin. 

One  may  easily  ascertain  the  presence  of  a  digestive 
ferment  in  the  juice  of  the  Pineapple  by  expressing  the 
juice,  filtering  and  placing  a  little  fibrin  in  it  (this,  if 
purchased  dry,  should  be  previously  softened  in  water) . 
Place  a  little  fibrin  in  water  as  a  control.  The  ferment 
of  Pineapple  works  best  in  alkaline  or  neutral  solution 
and  hence  resembles  trypsin  rather  than  pepsin. 


THE   WOBK  OF  LEAVES  173 

Food  is  used  in  two  ways:  (1)  as  a  source  of 
material  for  growth,  (2)  as  a  source  of  energy  for  do- 
ing work  and  keeping  the  living  machine  in  motion. 
The  energy  is  obtained  from  the  food  by  burning  it 
(just  as  in  an  engine:  see  page  35).  The  burning  or 
oxidation  is  accomplished  by  means  of  ferments  of 
various  kinds  which  abound  in  both  the  plant  and 
the  animal  organism. 

The  amount  of  energy  furnished  by  a  food  is  called 
the  fuel  value,  and  may  be  ascertained  by  measuring 
the  heat  produced  by  burning  it  directly  or  by  feeding 
it  to  an  animal  and  measuring  the  amount  of  heat 
given  off  by  the  body  during  a  given  time.  The  latter 
method  does  not  give  as  high  results  as  the  former, 
since  the  body  resembles  other  machines  in  not  getting 
the  full  theoretical  amount  of  energy  out  of  its  fuel 
(it  is,  however,  a  far  more  perfect  machine  in  this 
respect  than  most  machines  devised  by  man) :  more- 
over, not  all  the  energy  of  the  fuel  is  set  free  at  once 
as  heat,  since  a  certain  part  is  used  in  doing  mechanical 
work,  chemical  work,  etc.  The  fuel  value  of  proteids 
and  carbohydrates  is  in  general  about  the  same,  while 
that  of  fats  is  about  two  and  one-half  times  as  great. ^ 

Since  the  energy  is  obtained  from  the  food  by  burn- 

1  See  Peabody,  "Physiology  and  Anatomy,"  Chaps.  II  and  IV.  Also  the 
following  bulletins  of  the  U.  S.  Department  of  Agriculture.  "Foods;  Nutri- 
tion and  Cost,"  "Meats:  Composition  and  Cooking,"  "Milk  as  a  Food,"  "Sugar  as 
a  Food,"  "Fish  as  a  Food,"  "Food  and  the  Principles  of  Nutrition."  Also  arti- 
cles in  the  Year-Book  of  the  U.  S.  Dept.  of  Agriculture  for  1894,  by  Atwater 
(see  also  p.  547  ff.);  for  1902,  by  Milner  '..  for  1903,  by  Snyder  and  Woods. 


174  EXPEBIMENTS    WITH  PLANTS 

ing  or  oxidation,  and  since  the  carbon  is  the  principal 
substance  burned,  producing  a-^  the  final  result  carbon 
dioxide,  we  may  measure  the  carbon  dioxide  given  off 
by  an  organism  and  calculate  the  amount  of  carbon 
burned  and  consequently  the  amount  of  energy  used. 
Thus  it  has  been  found  by  experiment  that  burning  one 
gram  of  carbon  sets  free  about  eight  large  Calories^  and 
produces  about  two  liters  of  carbon  dioxide.  When- 
ever we  find  that  an  organism  has  given  off  two  liters 
(or  about  two  quarts)  of  carbon  dioxide,  we  know  that 
it  has  set  free  from  the  carbon  of  its  food  materials 
about  eight  large  Calories. ^  This  energy  can  be  used 
by  the  organism  in  the  form  of  heat,  chemical  work, 
mechanical  work,  etc.  If  the  whole  eight  large  Calories 
were  used  in  mechanical  work  they  would  suffice  to 
raise  (8  x  426  =)  3,408  kilograms  (=  about  7,500 
pounds)  one  meter  (=  about  39  inches  or,  roughly, 
1  yard) . 

We  may  look  at  the  matter  in  another  way.  Wlien 
an  organism  has  produced  its  own  weight  of  carbon 
dioxide  it  has  set  free  from  the  carbon  in  its  food 
enough  energy  to  raise  itself  about  600  miles.    A  man 

1  A  large  Calorie  is  the  amount  of  heat  needed  to  raise  the  temperature  of 
one  kilogram  (about  a  quart)  of  water  from  0°  to  1°  centigrade.  This  is  roughly 
the  amount  needed  to  raise  the  temperature  of  one  pound  (or  one  pint)  of  water 
through  4°  Fahrenheit. 

2  While  the  amount  of  energy  yielded  by  burning  a  gram  of  carbon  differs 
somewhat,  depending  on  whether  the  carbon  at  the  start  is  in  the  form  of  char- 
coal, starch,  fat  or  proteid,  the  difference  is  not  large  enough  to  affect  the 
calculation  here  given. 


TEE    WORK   OF   LEA  VES  175  > 

exhales  in  twenty- four  hours  carbon  dioxide  amount- 
ing to  about  1.2  per  cent  of  his  own  weight,  while 
some  bacteria  give  off  in  the  same  length  of  time  twice 
their  own  weight  of  carbon  dioxide.  It  should  be 
remembered  that  foods  contain  other  combustible  sub- 
stances besides  carbon  (e.  g.,  hydrogen),  and  that  the 
above  figures  leave  out  of  account  the  energy  liberated 
by  burning  these  substances.  They  do  not,  therefore, 
indicate  the  total  amount  of  energy  set  free,  but  only 
the  principal  part. 

By  the  method  illustrated  in  Fig.  31,  we  can 
measure  approximately  the  volume  of  carbon  dioxide 
given  off,  and  from  this  calculate  the  amount  of  energy 
set  free  from  the  carbon  of  the  food  in  a  given  time. 
We  may  also  find  the  weight  of  the  carbon  dioxide 
(one  liter  of  carbon  dioxide  weighs  about  two  grams) , 
and  so  calculate  how  far  the  energy  set  free  would 
raise  the  organism  if  applied  as  mechanical  energy. 
Make  these  calculations  in  the  experiment  described 
on  page  34  (Fig.  31) .  The  experiment  may  be  modi- 
fied by  setting  the  bottle  containing  the  seeds  upright 
and  bending  the  tube  which  passes  through  the 
stopper  so  as  to  make  its  free  end  dip  into  a  vessel 
containing    lye. 

The  giving  off  of  carbon  dioxide  is  accompanied 
by  the  absorption  of  oxygen :  this  process  is  called 
respiration:  it  occurs  in  every  living  cell,  since  every 
such  cell   has   need  of  energy  to  perform   its   work. 


176  EXPERIMENTS    WITH  PLANTS 

In  plants  each  cell  probably  absorbs  its  oxygen 
directly  from  the  air,  which  penetrates  all  parts  of 
the  plant:  in  insects  a  somewhat  similar  method  is 
found,  in  that  branching  tubes  convey  the  air  to  all 
the  viscera  ;  while  in  animals  the  air  is  conveyed  to 
the  lungs,  absorbed  by  the  moist  membranes  of  the 
lung  tissue,  whereupon  the  oxygen  combines  with  the 
red  coloring  matter  (haemoglobin)  of  the  blood, 
changing  it  from  dark  to  bright  red.  The  haemo- 
globin is  carried  to  all  parts  of  the  body  (principally 
in  the  arteries),  where  it  gives  up  its  oxygen  to  the 
various  tissues  and  is  thereby  changed  back  to  dark 
red  and  returns  to  the  lungs  (principally  through  the 
veins)    for  a  fresh   supply. 

While  both  plants  and  animals  need  all  three  kinds 
of  food,  i.  e.,  proteids,  fats  and  carbohydrates  (sugars 
and  starch),  they  require  them  in  different  propor- 
tions. In  dietetics  proteids  are  spoken  of  as  flesh- 
or  muscle -formers,  while  starch,  sugars  and  fats 
are  said  to  furnish  fuel.  This  is  not  by  any  means 
true  absolutely,  but  it  is  probably  so  in  the  main. 
The  animal  needs  much  more  nitrogen-containing  food 
(proteid)  than  the  plant:  the  animal  excretes  large 
quantities  of  nitrogen  (in  the  urine  and  feces),  while 
the  plant  excretes  none.  It  is  interesting,  in  this  con- 
nection, to  compare  the  composition  of  the  food  con- 
tained in  seeds  with  that  contained  in  eggs.  While 
the  white  of  a  hen's  Qg^,  for  example,  is  almost  pure 


THE    WORK  OF  LEAVES  177 

proteid,  the  yolk  is  largely  fat  and  oil.  The  ^gg 
(minus  the  shell)  contains  about  14  per  cent  of  pro- 
teid and  13  of  fat;  this  is  a  higher  percentage  of 
proteid  than  most  seeds  possess,  but  Peas,  Beans, 
etc.,  contain  as  much  as  24  per  cent  of  proteid:  in 
oily  seeds,  fat  may  be  present  to  the  amount  of  60 
per  cent. 

Of  especial  interest  is  the  composition  of  Grains; 
as  an  example  of  these  we  may  take  Wheat.  Moisten 
some  ordinary  Wheat  flour  with  water  and  place  it 
in  a  muslin  bag.  Allow  a  stream  of  water  to  run 
slowly  through  the  bag  while  the  dough  is  kneaded 
with  the  fingers.  Collect  the  milky  fluid  which  runs 
through  the  cloth:  this  contains  the  starch,  which 
gradually  settles  to  the  bottom.  When  the  starch  is 
all  removed  there  remains  behind  a  mass  which,  from 
its  glutinous  consistency,  is  called  gluten:  this  is  the 
proteid  of  the  Wheat  (apply  the  proteid  tests  to  it). 
It  forms  about  10  per  cent  of  the  flour,  while  the 
starch  forms  about  75  per  cent. 

Take  some  grains  of  Wheat  which  have  been  suffi- 
ciently softened  in  water  (a  few  minutes  suffices  in  hot 
water)  to.  cut  easily,  and  with  a  razor  cut  thin  slices 
across  the  grain.  Place  some  of  these  in  a  drop  of 
water  on  a  glass  slide,  cover  with  a  cover- glass,  and 
examine  with  the  low  power  of  the  microscope.  Re- 
move the  cover -glass  and  add  a  drop  of  iodine  solu- 
tion.   Notice  the  blue-black  color  of  the  internal  part 


178  EXPERIMENTS    WITH  PLANTS 

of  the  gram  and  the  intense  brown  or  yellowish  brown 
of  the  peripheral  layer.  Place  another  section  on  a 
slide,  remove  all  superfluous  moisture  with  blotting 
paper,  and  place  upon  it  a  drop  of  a  saturated  solution 
of  cane-sugar  in  water.  Then  add  a  small  drop  of 
chemically  pure  sulphuric  acid  (by  means  of  a  pipette 
or  medicine -dropper).  Add  a  second  drop  of  acid  if 
necessary ;  use  no  cover-glass ;  be  careful  that  no  acid 
is  spilled  upon  the  microscope.  Notice  the  bright  red 
color  of  the  peripheral  layer;  this  indicates  the  pres- 
ence of  proteid.  The  outer  peripheral  layer  is  much 
richer  in  proteid  than  the  rest  of  the  grain:  owing  to 
its  dark  color  it  is  considered  undesirable  for  flour  and 
is  separated  from  the  rest  of  the  grain  in  milling, 
forming  the  bran,  so  that  ordinary  Wheat  flour  consists 
of  the  internal  part  of  the  grain  only.  As  the  bran 
forms  about  one-fifth  of  the  grain,  this  is  a  wasteful 
process.  Whole  Wheat  flour  contains  the  bran  as  well 
as  the  inner  portion  and  is  not  only  more  nutritious 
but  more  easily  digested  and  more  healthful  in  other 
respects.  Find  out  what  you  can  about  the  process  of 
milling  and  the  use  of  flour  in  bread,  etc.^ 

Note  the  great  difference  between  the  seed-leaves  of 
the  Horse-bean  (Fig.  2)  and  the  Castor-bean  (Fig.  4). 
Can   you   explain    this   difference   of    structure    on    the 

1  See  Johnson,  "Chemistry  of  Common  Life,"  Chap.  V  ;  Williams,  "Chem- 
istry of  Cookery,"  Chap.  XH  ;  Williams  and  Fisher,  "Theory  and  Practice  of 
Cookery."  Also  an  article  by  Snyder  and  Woods  in  the  Year-Book  of  the  U.  S. 
Dept.  of  Agriculture,  for  1903. 


THE    WOBK  OF  LEAVES  179 

ground  of  difference  in  function  ?  The  Horse-bean  seed- 
leaves  are  very  thick  and  gorged  with  food;  those  of 
the  Castor- bean  are  extremely  thhi  and  contain  prac- 
tically no  food:  on  the  contrary,  the  nutriment  (en- 
dosperm) is  packed  around  them  and  it  is  their  task 
to  absorb  it.  For  this  purpose  they  are  closely  and 
firmly  attached  to  it  and  are  provided  with  veins 
which  help  to  convey  the  nutriment  directly  to  the 
germ.  As  soon  as  germination  begins  they  enlarge, 
and  so  increase  their  absorptive  surface,  and  they 
continue  to  absorb  the  nutriment  long  after  they  have 
come  above  ground.  When  the  food  has  entirely 
disappeared  the  husk  falls  away,  leaving  the  seed- 
leaves  free. 

The  Corn  has  a  seed-leaf  (Fig.  6,  I)  which  is  both 
a  storehouse  and  an  absorbing  organ ;  it  is  the  small 
white,  shield- shaped  portion  of  the  germ  which  is 
closely  applied  to  the  starchy  endosperm  (the  endo- 
sperm is  shaded  in  the  figure) .  If  Sugar  Corn  can  be 
obtained,  a  drop  of  iodine  will  show  that  the  endo- 
sperm contains  little  or  no  starch,  while  the  seed-leaf 
is  gorged  with  it.  Remove  the  endosperm  from  ger- 
minating plants  of  Corn  and  Castor- bean,  and  com- 
pare their  subsequent  growth  with  that  of  uninjured 
control  plants. 

What  other  familiar  seeds  have  endosperm  and  ab- 
sorbent seed-leaves?  Notice  the  curious  seed-leaf  of 
the    Cocoanut    (Fig.    45),   which   consists    of    a   soft, 


180 


EXPERIMENTS    WITH   PLANTS 


100.  Germi- 
nating Date, 
showing  the 
large  absorb- 
ent seed-leaf 
(si). 


spongy  mass,  traversed  by  fibrous  veins 
whioh  convey  the  food.  At  first  it  is  very 
small,  but  grows  rapidly  during  germina- 
tion and  soon  fills  the  whole  cavity.  It  ab- 
sorbs the  milk  and  then  the  meat  of  the 
Cocoanut  (both  of  these  together  make  up 
the  endosperm,  which  is  partly  solid  and 
partly  liquid) .  Study  also  the  germination 
of  the  Date  (Fig.  100),  which  resembles 
that  of  the  Cocoanut  in  the  formation  of 
a  large  absorbing  organ. 

Between  the  seed-leaves  and  the  next 
leaves  produced  by  the  plant,  i.  e.,  the 
foliage -leaves,  there  is  a  great  contrast  in 
appearance.  Some  of  the  differences  be- 
tween the  two,  in  the  Horse-bean,  are  as 
follows : 


Seed-leaves 


Small 

Thick 

Pale  yellow 

Underground 

Gradually  grow  smaller 

Fall  off  after  a  time 

Obscurely  veined 

No  stalk 

No  stipules  (appendages  at 

base  of  stalk) 
Brittle ;  not  fibrous 
Opposite 


Foliage-leaves : 
Large 
Thin 

Bright  green 
Above  ground 
Gradually  grow  larger 
Remain  on  a  long  time 
Conspicuously  veined 
Stalked 
Stipules  present 

Tough  and  fibrous 
Alternate 


THE    WORK  OF  LEAVES  181 

Can  you  explain  these  differences  of  structure  as  due 
to  differences  in  function  ?  What  is  the  function  of  the 
foliage-leaves?  Remove  the  foliage -leaves  (a)  from 
some  young  plants  which  have  not  yet  exhausted  the 
supply  of  food  in  their  seed-leaves;  {h)  from  some  older 
plants  in  which  this  supply  is  exhausted  and  from 
which  the  seed-leaves  have  fallen  away;  in  each  case 
have  control  plants  for  comparison.  Does  the  removal 
of  the  leaves  check  the  growth?  In  which  of  the  two 
cases  {a)  or  {h)  is  this  most  apparent?  Does  the  result 
indicate  that  the  foliage-leaves,  like  the  seed-leaves, 
nourish  the  plant  ? 

Do  the  foliage-leaves,  like  the  seed-leaves,  contain 
food?  Remove  some  foliage -leaves  from  a  healthy, 
vigorous  plant,  preferably  one  which  grows  out  of 
doors,  with  a  good  exposure  to  sunlight  (a  Nasturtium 
is  excellent  for  this  purpose).  Remove  some  of  the 
leaves  at  sundown.  Boil  them  in  water  as  soon  as 
removed  and  place  them  in  alcohol;  let  them  remain 
in  it  until  the  green  coloring  matter  is  extracted. 
When  this  is  accomplished  (twelve  to  twenty-four 
hours  is  ususually  sufficient),  rinse  in  water,  and  place 
them  in  watery  iodine  solution.  Do  you  find  starch 
pi-esent?  (The  other  tests  mentioned  on  pages  164  and 
165  may  also  be  made ;  the  sugar  test  should  be  made 
on  sap  expressed  from  the  fresh  leaves;  the  test  for 
oils  and  fats  on  leaves  dried  without  being  placed  in 
alcohol.) 


182 


EXPERIMENTS    WITH   PLANTS 


Does  this  starch  come  from  the  supply  stored  up  in 
the  seed-leaves,  or  is  it  manufactured  in  the  foliage-leaf? 

Keep  a  plant  in  darkness  ^  until  the 
leaves  no  longer  give  a  starch  test, 
then  cut  off  several  leaves  and  place 
them  in  tumblers  of  water;  place 
one -half  the  number  in  sunlight  and 
the  other  half  in  darkness;  take 
care  that  the  stalk  (but  not  the 
blade)  of  the  leaf  dips  under  the 
water  (Fig.  101).  In  two  or  three 
days  test  the  leaves  which  have 
been  in  the  light.  Do  you  find  any 
starch  ?  This  starch 
must  have  been  made 
hy  the  leaves  after  they 
were  removed  from  the 
'plant.  Now  test  those  which  have  been 
in  darkness.  Is  the  difference  due  to  the 
absence  of  light?  We  may  put  this  to  a 
final  test  in  a  very  simple  way.  Pin  corks 
to  the  opposite  sides  of  a  leaf,  as  shown 
in  Fig.  102,  so  as  to  completely  exclude 
light  from  the  covered  portion;  over  an- 
other leaf  put  tin-foil  so  as  to  cover  both 
sides,  having  first  cut  out  letters  or  figures 
from  the  tin -foil   on  the    upper   surface; 


101.  Leaf  of  English  Ivy 
deprived  of  starch  and 
placed  in  water,  to  see  if 
it  can  make  starch  when 
separated  from  the  plant. 


102.  Arrange- 
ment for  ex- 
cluding .  light 
from  a  part  of 
the  leaf. 


'  The  plant  may  be  covered  with  a  box  or  a  cone  made  of  pasteboard. 


THE    WOBK    OF   LEA  VES  183 

The  cork  or  tin -foil  must  not  be  applied  so  closely  as 
to  prevent  the  free  circulation  of  air  between  it  and 
the  leaf.  The  leaves  must  not  be  removed  from  the 
plant  and  should  be  placed  where  they  may  obtain 
abundant  sunlight;  Nasturtium  leaves  may  be  recom- 
mended for  this  experiment.  In  two  or  three  days  test 
for  starch. 

Now  of  what  use  is  the  starch  in  the  foliage- 
leaves  ?  Is  it  absorbed  by  the  plant,  like  the  starch  in 
the  seed-leaves?  If  so,  ought  we  not  to  find  less  starch 
in  the  leaves  in  the  morning  than  at  sundown  (since 
the  starch  which  is  taken  away  from  the  leaf  during 
the  night  cannot  be  replaced  until  it  is  again  exposed 
to  light)?  Remove  some  leaves  from  a  plant  near  sun- 
down and  place  them  in  alcohol ;  early  the  next  morn- 
ing remove  some  more  leaves  from  the  same  plant  and 
test  both  sets  of  leaves  for  starch.  We  may  also  make 
the  experiment  by  cutting  out  a  sample  from  a  leaf  £tt 
sundown,  to  be  compared  with  a  sample  taken  from 
the  same  leaf  the  next  morning.  Has  the  starch  disap- 
peared ?  Would  it  have  done  so  had  the  leaves  not 
been  left  on  the  plant!  Repeat  the  experiment,  but  cut 
the  leaves  off  and  leave  them  over  night  in  a  tumbler 
of  water  (the  stalks  must  dip  well  under  the  water) . 

It  is  now  time  to  see  whether  we  can  answer  the 
question,  Why  are  the  foliage-leaves  and  seed-leaves  (of 
the  Horse-bean)  so  different?  You  can  see  that  it  is  of 
advantage  to  the  plant  to  have  the  foliage -leaves  re- 


184  EXPERIMENTS    WITH  PLANTS 

main  as  long  as  possible  on  the  plant.  You  can  also 
see  why  they  should  have  as  large  a  surface  as  they 
can,  since  the  more  light  they  catch  the  more  starch 
they  can  make.    You  can  see,  too,  why  the  seed-leaves 


103.    Two  lots  of  Squash  seedlings  of  the  same  age.    Those  on  the  left  were  grown  in 
the  light,  those  on  the  right  in  the  dark. 

need  to  be  thick  and  bulky,  so  as  to  store  up  a  great 
deal  of  starch.  The  reasons  for  the  other  differences  in 
structure  will  become  apparent  as  we  go  on.  Perhaps 
you  do  not  see  why  the  foliage -leaves  are  green  and 
the  seed-leaves  pale  yellow.  You  will  understand  this 
if  you  put  a  few  seeds  into  a  pot  containing  soil  or  saw- 
dust and  keep  it  entirely  in  the  dark  until  the  plants 


THE    WORK  OF  LEAVES  185 

are  several  inches  high.  The  plants  grow  very  tali 
and  slender  and  the  leaves  are  small  and  yellow,  re- 
sembling the  seed-leaves  in  color  (Fig.  103).  Put  the 
plants  in  the  light  for  a  day  or  so.  Test  them  for 
starch.  Leave  them  in  the  light  until  they  turn  green. 
Then  test  again  for  starch.  Does  the  result  indicate  that 
the  green  substance  is  necessary  for  making  starch?^ 
It  is  this  substance,  called  leaf-green,  or  chlorophyll, 
which  is  extracted  by  the  alcohol  when  you  test  the 
leaves  for  starch.  Usually  it  is  not  formed  in  darkness. 
Do  you  now  see  why  the  seed-leaves  are  not  green  ? 
Eemove  some  of  the  earth  so  as  to  expose  them  to  the 
light.    Do  they  turn  green  ? 

The  seed-leaves  and  foliage -leaves  are  different  be- 
cause they  have  different  tasks  to  perform,  and  their 
structure  must  be  adapted  to  the  special  kind  of  work 
they  have  to  do.  We  may  sum  this  up  by  saying, 
function  determines  structure. 

A  good  illustration  of  this  is  seen  in  the  history  of 
the  Castor- bean  seed-leaves.  At  first  they  are  absorb- 
ing organs,  pure  and  simple,  and  their  structure  is 
admirably  adapted  to  the  work  they  have  in  hand. 
Later,  when  they  come  to  do  the  work  of  foliage-leaves, 
they  grow  much  larger,  thicker,  tougher  and  more 
fibrous.  They  spread  out  above  ground  in  a  position  to 
catch  the  light  (Fig.  104),  and  their  internal  structure 

1  Find  out  whether  leaves  variegated  with  white  spots  make  starch  in  the 
colorless  portions. 


186 


EXPERIMENTS    WITH   PLANTS 


w 


) 


becomes  greatly  modified  so  as  to  be  like  that  of  foli- 
age-leaves. At  the  same  time  they  acquire  a  green 
color  and  begin  to  manufactm-e 
starch. 

This  principle  is  so  general  that 
we  are  justified  in  looking  for  similar 
structures  wherever  similar  functions 
occur. 

Of  what  is  starch  made?  We  may 
get  some  indication  of  this  by  decom- 
posing starch  by  means  of  heat  in 
the  apparatus  shown  in  Fig.  105.  If 
a  test-tube  is  not  obtainable,  use  any 
piece  of  glass  tubing  (the  thinner  it 
is  the  less  liable  it  is  to  crack) 
sealed  at  one  end.  Place  the  starch 
in  it  and  heat  slowly.  When  the  starch  begins  to 
turn  brown,  water  will  col- 
lect on  the  sides  of  the 
tube  ;  this  also  takes  place 
if  we  dry  the  starch  to  con- 
stant weight,  at  the  tem- 
perature at  which  water 
boils,  before  beginning  the 
experiment .  The  water 
must,  therefore,  result  from 

the       decomposition      of      the     lo-,.    Apparatus  for  the  decomposition  bt 
.  ^  -r  a  1        i.     4-1  sturch;  the  giises  pass  into  a  tumbler 

starch.    It   we   conduct  the       of  ume-water. 


104.  A  seedling  of  Castor- 
bean,  showing  how  the 
seed-leaves  assume  the 
form  and  function  of 
foliage-leaves. 


THE    WO  UK   OF   LEAVES 


187 


gases  over  into  lime-water,  as 
shown  in  the  figure,  it  will  soon  ])ecome 
milky.  The  starch,  therefore,  appears 
to  break  up  into  water  and  carbon  di- 
oxide. What  other  substances  may  be 
formed  we  cannot  determine  with  the 
means  at  our  disposal,  but  these  may 
be  neglected,  since  chemical  analysis 
shows  that  starch  may  be  considered  to 
result  from  the  union  of  these  two  sub- 
stances. 

The  question  now  arises,  Is  there  any 
evidence  that  the  plant  makes  starch  by 
putting  carbon  dioxide  and  water  to- 
gether ?  We  know  from  previous  experi- 
ments that  there  is  carbon  dioxide  in  the 
air,  since  lime-water  exposed  to  air  soon 
forms  a  precipitate  on  the  surface.  We 
also  know  that  the  leaf  is  well  supplied 
with  water.  Is  it  well  supplied  with  air? 
The  best  way  to  answer  this  question  is 
to  place  the  leaf  in  an  air-pump,  which 
we  may  construct  as  shown  in  Fig.  106. 
A  disk  of  rubber  (leather  or  I'awhide 
may  be  used)  is  fitted  to  the  inside  of 
a  student  -  lamp  chimney  (the  larger 
size.  No.  1,  is  preferable),  and  pushed 
down  to  the  neck  of  the  chimney.    The 


106. 
Air  -  pump 
made  from 
a  lampchim- 
ney, umbrella 
wire  and  rub- 
ber stopper. 


188 


JSXPEBIMENTS    WITH  PLANTS 


chimney  is  now  inverted,  the  enlarged  base  is  then 
carefully  warmed  and  melted  sealing-wax  poured  in  to 
the  depth  of  an  inch  or  more.  A  slightly  larger  disk 
of  rubber  is  now  prepared  by  fitting  a  rubber  stopper 
into  the  small  end  of  the  chimney  and 
cutting  a  slice  from  it  just  above  the 
chinniey's  edge  (leather  may  be  used  if 
rubber  is  not  available).  This  rubber 
disk  (r)  is  to  be  impaled  on  an  um- 
brella wire,  as  shown  in  Fig.  107  (the 
larger  of  its  surfaces  is  to  be  upper- 
most), and  firmly  supported  on  one 
side  by  a  wooden  disk  {w) .  The  end 
^  of  a  spool  is  excellent  for  this  purpose ; 
it  should  be  trimmed  down  to  such 
dimensions  that  it  will  slip  easily  into 
the  chimney.  Below  the  wooden  disk 
we  place  a  little  sealing-wax  to  keep  it 
from  slipping  off  ;  above  the  rubber 
disk  we  also  place  sealing-wax,  as 
shown  in  the  figure.  All  the  joints 
must  be  made  air-tight  with  sealing-wax  ;  this  is 
facilitated  by  filling  the  core  of  the  spool  with  seal- 
ing-wax, sharpening  the  end  of  the  wire,  heating  it 
and  forcing  it  through  the  center  of  the  rubber  disk, 
and  then  through  the  core  of  the  spool.  We  must  not 
be  discouraged  by  a  few  failures  in  constructing  the 
apparatus,  since,  after  a  little  practice,  we  shall  be  able 


107.    Details  of  piston 
of  air-pump. 


THE    WORK   OF  LEAVES  189 

to  make  one  successfully  in  a  few  minutes.  When 
these  arrangements  are  complete,  apply  vaseline  to  the 
edges  of  the  rubber  disk  and  mouth  of  the  chimney 
(this  precaution  is  important).  Pour  some  water 
into  the  chimney  and  force  the  piston  slowly  down 
until  the  water  stands  half  an  inch  or  so  above  the 
piston;  the  rubber  bends  back  as  it  is  forced  down, 
allowing  the  air  to  escape;  when  the  piston  is  drawn 
upward  the  wooden  disk  prevents  it  from  bending  and 
so  keeps  the  air  from  entering.  Pull  the  piston  back 
nearly  to  the  top  of  the  chimney  and  secure  it  by 
means  of  a  clothes-pin,  as  shown  in  the  figure;  a  lump 
of  sealing-wax  fastened  to  the  wire  above  the  clothes- 
pin prevents  it  from  slipping  back.  Any  leaks  in  the 
piston  may  now  be  detected  by  inverting  the  chimney; 
they  may  be  stopped  with  sealing-wax  if  they  occur  in 
the  joints;  if  the  leak  occurs  around  the  edge  of  the 
rubber  disk  a  larger  one  must  be  substituted.  On  the 
other  hand,  the  trouble  may  result  from  having  too 
large  a  rubber  disk,  in  which  case  it  will  not  lie  flat 
and  a  smaller  one  must  be  substituted.  In  withdraw- 
ing the  piston  from  the  chimney,  it  is  advisable  to 
draw  it  out  slowly,  with  a  twisting  motion. 

A  somewhat  more  convenient  form  of  piston  may 
be  made  by  a  mechanic,  after  the  plan  shown  in  Fig. 
108.  It  consists  of  a  brass  rod  (about  one-fourth  of  an 
inch  thick),  with  a  thread  at  the  end  carrying  two 
nuts  (Fig.  109,  >^,w),  a  small  washer  (^^),  and  a  brass 


190 


EXPERIMENTS    WITH   PLANTS 


disk  {d)  which  supports  the  rubber  disk  (r) .  It  has 
the  advantage  of  allowing  a  quick  change  of  the 
rubber.    Through  a  small  hole  about  four  inches  above 


A 


-^. 


-n 


109.  Details  of  piston  of  the 
air  -  pump  shown  in  Fig. 
108:  (r)  rubber  disk,  (rf) 
metal  disk,  {iv)  washer, 
(«)  nut. 


the     rubber     passes     a 

stout     piece     of     piano 

wire  (or  any  steel  wdre 

suitable     for     springs) , 

which  is  bent  as  shown 

in  the  figure  and  has  its 

ends  passed  through  an- 
other hole  about  an  inch 

above  the  rubber.  When 

the  piston  is  drawn  up, 

the     wire     springs    out 

and   prevents    it   from    slipping   back. 
When  the   apparatus  is  ready,  place  a 

leaf  in  the  chimney  and  cover  it  with  water. 

Force   the    piston    down    slowly   until    the 

water  stands  half  an  inch  or  so  above  it, 

and  then  pull  it  up  and  secure  it  in  place. 
Does  air  issue  from  the  leaf?  If  so.  at  what  points? 
Notice  especially  whether  more  air  issues  from  the 
upper  or  from  the  lower  surface.  Allow  it  to  remain 
until  all  the  air  is  drawn  out,  making  another  stroke 
with  the  piston  if  necessary.  Notice  the  appearance 
of  the  leaf  when  injected  with  water.  Explain  its  close 
resemblance  to  a  leaf  which  has  been  boiled. 

If  we  prevent  air  from  entering  the  leaf,  how  will  it 


108.  Air  •  pump 
with  a  u  t  o  - 
matic  arrange- 
ment to  pre- 
vent the  pis- 
ton from  slip- 
ping back. 


TRE    WOh'K   OF   LEA  VES 


191 


affect  starch  formation  ?  Keep  a  i)laiit  in  the  dark  until 
the  leaves  no  longer  give  a  good  starch  test.  Remove 
the  plant  to  the  light  and  treat  several  of  its  leaves  by 
covering  both  sides  of  a  portion  of  the  leaf  with  vase- 
line. Remove  some  of  the  untreated  leaves  from  the 
plant,  and  place  them  in  tumblers  of  water  so  that  the 
stalk  of  the  leaf  and  about  half  of  the  blade  dip  under 
water.  Place  all  of  the  leaves  where  they  will  get 
abundant  sunlight.  In  two  or  three  days,  test  all  the 
leaves  for  starch  (removing  them  from  the  plant  at 
sundown).  Do  you  find  starch  in  the  portions  from 
which  air  has  been  excluded  ? 

Does  the  leaf  decompose  carbon  dioxide?  Invert  a 
large  bottle  or  fruit -jar,  as  shown  in  Fig.  110,  over  a 
lighted  candle  set  in  a 
cork  floating  on  water. 
After  a  short  time  the 
candle  goes  out,  indicat- 
ing that  some  of  the 
oxygen  of  the  air  has 
been  converted  by  burn- 
ing into  water  and  car- 
l)on  dioxide.  Withdraw 
the  candle  by  means  of  a  string  attached  to  it  and 
introduce  a  leaf,  the  stalk  of  which  passes  through  a 
hole  in  the  center  of  a  cork,  as  shown  in  the  figure:  do 
this  without  lifting  the  bottle  above  the  surface  of  the 
water..    The  experiment  should  be  commenced  in  the 


110.  Arrangement  for  investigating  the  power 
of  a  leaf  to  "  restore  "  air  which  has  been 
"vitiated"  by  a  burning  candle.  (Sec- 
tional view.) 


192 


EXPERIMENTS    WITH  PLANTS 


i 


morning  and  continued  until  near  sundown  (the  leaf 
should  receive  sunshine  in  the  meanwhile:  prolong  the 
experiment  two  days  if  necessary).  We  then  lift 
the  jar  very  carefully,  so  as  not  to 
admit  any  air,  and  introduce  a  lighted 
candle,  as  before.  If  it  does  not  imme- 
diately go  out,  it  indicates  that  some  of 
the  carbon  dioxide  has  been  absorbed 
by  the  leaf  and  decomposed,  with  the  re- 
sult that  oxygen  is  set  free,  so  that 
further  combustion  is  possi- 
ble. As  a  control  use  a 
bottle  with  no  leaf  in  it. 

Chemical  analysis  shows 
that  if  carbon  dioxide  and 
water  unite  to  form  starch, 
oxygen  must  be  given  off,  just 
as  we  have  found  in  this  ex- 
periment. Another  way  of 
testing  this  matter  is  shown 
in  Fig.  111.  A  plant  which 
naturally  grows  submerged  in 
water  is  put  into  water  in  a 
glass  jar  and  placed  in  sun- 
light. The  gas  evolved  is  col- 
lected in  the  funnel,  which  is 

111.    Arrangement  for  collecting  the      first   filled    with    Watcr    by  SUb- 
^^^uo^^.y...i.r.^l.niin      ^^^^^^J^g       ^^      aud       COrkiug      it 


THE    WORK   OF   LEA  VES 


193 


under  water.  When  sufficient  gas  has  collected,  the 
cork  is  removed  from  the  neck  and  a  glowing  splinter 
is  quickly  thrust  into  the  neck.  If  it  glows  more 
brightly  or  bursts  into  flame,  it  indi- 
cates that  the  gas  in  the  funnel  is  richer 
in  oxygen  than  ordinary  air,  and, 
consequently,  that  the  plant  is  giving 
off  oxygen. 

These  results,  taken  in  connection 
with  the  fact  that  the  formation  of 
starch  is  prevented  by  depriving  the 
leaf  of  air,  make  it  highly  probable  that 
the  leaf  makes  starch  by  causing  car- 
bon dioxide  and  water  to  unite,  accom- 
panied by  the  giving  off  of  oxygen. 
It  would  lend  greater  certainty,  how- 
ever, if  we  could  deprive  the  leaf  of 
carbon  dioxide  without  at  the  same 
time  depriving  it  of  the  other  constitu- 
ents of  air.  We  may  do  this  by  means 
of  the  apparatus  shown  in  Fig.  112. 
fruit -jar  is  fitted  with  a  stopper  of  cork  or  wood, 
through  which  passes  a  funnel  filled  with  lumps  of 
lye  which  will  absorb  the  carbon  dioxide  from  the 
air  as  it  enters  the  bottle.  On  the  bottom  of  the  bottle 
we  place  some  lumps  of  lye  and  a  small  bottle  of 
water  in  which  is  a  leaf  of  Nasturtium  (or  some  other 
Jeaf  which  normally  gives  a  good  starch  test)  which  has 


112.  Apparatus  for 
growing  a  leaf  in 
air  deprived  of  car- 
bon dioxide:  lumps 
of  lye  are  placed  in 
the  funnel  and  on 
the  bottom  of  the 
bottle. 


A   bottle   or 


M 


194  EXPElilMEXTS     WITH   PLANTS 

been  deprived  of  starch  in  tlie  way  previously  described. 
Place  the  stopper  in  position  and  close  all  joints  air- 
tight with  vaseline.  Prepare  a  control  in  which  the 
lye  is  replaced  by  some  indifferent  substance,  such  as 
pebbles  or  broken  glass.  After  a  day  or  so  of  expo- 
sure to  sunlight,  test  both  leaves  for  starch.  Has  the 
leaf  which  is  deprived  of  carbon  dioxide  (but  not  of 
the  other  constituents  of  the  air)  been  able  to  make 
starch  ? 

The  leaves,  by  their  power  of  giving  off  oxygen, 
"restore"  foul  air  and  make  it  fit  for  animals  to 
breathe;  this  is  especially  noticeable  in  aquaria  where, 
if  a  proper  balance  be  struck  between  animal  and 
vegetable  life,  the  air  contained  in  the  water  does  not 
need  to  be  renewed.  Ordinary  air  contains  about  four- 
hundredths  of  one  per  cent  carbon  dioxide.  It  is  calcu- 
lated that  a  square  meter  of  ordinary  leaf  surface 
decomposes  every  hour  in  sunlight  as  much  carbon 
dioxide  as  is  contained  in  1,000  liters  of  air.  To  offset 
this,  carbon  dioxide  is  continually  poured  into  the  air 
by  combustion  of  all  kinds  as  well  as  by  the  respira- 
tion of  plants  and  animals.  We  have  learned  (pages 
34  and  142)  that  roots  and  germinating  seeds  give  off 
carbon  dioxide  just  like  animals.  Leaves  give  off  oxygen 
only  in  the  sunlight.  Do  they  give  off  carbon  dioxide  at 
other  times,  just  as  roots  do  ?  We  may  easily  investi- 
gate this  by  partly  filling  a  bottle  or  jar  wdth  water, 
putting  in  as  many  leaves  (with  their  stalks  dipping  in 


THJS    WORK   OF   LEA  VES  195 

water)  as  it  will  conveniently  hold,  and  then  inserting 
a  small  vial  partly  filled  with  clear  lime-water.  Set 
the  bottle  away  for  a  day  or  two  in  darkness.  Prepare 
a  control  bottle  in  which  no  leaves  are  placed.  Both 
bottles  should  be  sealed  air-tight.  In  which  is  more 
carbon  dioxide  produced,  as  shown  by  the  lime-water 
test?  As  the  result  of  this  experiment  we  may  say 
that  in  the  dark  a  green  plant  behaves  in  regard  to 
respiration  like  a  colorless  plant  or  an  animal. 

There  is  a  popular  belief  that  plants  are  unhealth- 
ful  in  sick-rooms  at  night  because  they  vitiate  the  air. 
As  a  matter  of  fact,  it  would  take  a  very  large  number 
of  plants  to  do  as  much  harm  in  this  respect  as  a 
single  candle. 

Since  the  leaves  have  work  to  perform  during  the 
day,  as  well  as  during  the  night,  we  should  expect  to 
find  the  process  of  combustion  going  on  then  also,  since 
it  is  this  which  furnishes  energy  to  do  work ;  yet  we 
have  found  that  carbon  dioxide  is  used  up  and  oxygen 
produced  by  the  leaves  in  daylight.  Careful  determina- 
tion of  the  relative  amounts  of  the  gases  has  shown 
that  both  processes  take  place  simultaneously;  the 
sunlight  furnishes  energy  for  the  work  of  starch- 
making  which  results  in  the  production  of  oxygen ;  the 
combustion  which  results  in  the  production  of  carbon 
dioxide  furnishes  energy  for  work  of  other  kinds. 

Since  the  energy  which  is  absorbed  in  the  making 
of  starch  is   all   given   out   again  when   the   starch  is 


196  JSXPEBIMENTS    WITH   PLANTS 

burned,  it  may  be  considered  to  be  equal  to  the  heat  of 
combustion  (or  "fuel  value"  of  starch)  which  is  about 
4.5  large  Calories  for  every  gram  of  dry  starch.  If  we 
estimate  that  a  square  meter  of  leaf  surface  produces 
one  gi-am  of  dry  starch  every  hour  in  sunlight,  it  must 
in  so  doing  absorb  the  energy  of  the  sunlight  to  the 
extent  of  about  4.5  large  Calories.  But  this  amounts 
to  only  about  one -half  of  one  per  cent  of  the  total 
energy  which  falls  upon  it  during  that  time  in  the  form 
of  sunshine.  It  should  be  noted  that  it  is  principally 
the  red  rays  which  bring  about  the  chemical  changes 
here  considered,  just  as  in  the  eye  they,  more  than 
others,  bring  about  the  chemical  changes  which  result 
in  the  sensation  of  sight,  and  for  that  reason  appear 
much  brighter  to  the  eye  than  the  blue  rays.  The 
latter,  as  is  well  known,  are  the  ones  which  bring 
about  the  chemical  changes  in  a  photographic  plate. 
What  is  the  nature  of  the  openings  through  which  the 
air  passes?  With  a  sharp  knife,  make  a  shallow  cut 
and  tear  off  a  small  piece  of  the  delicate,  semi-trans- 
parent epidermis  from  the  lower  surface  of  the  leaf,^ 
place  it  on  a  glass  slide  in  a  drop  of  water  and  cover 
with  a  thin  cover- glass.  Examine  first  with  the  low 
(one-half  inch  or  two-third  inch  objective)  and  then 
with  the  high  power  (one-sixth  inch  or  one-eighth  inch 
objective)  under   a    compound  microscope.    The  epi- 

iThe  best  leaves  for  this  purpose  are  those  of  a  Lily  (or  any  plant  of  the 
Lily  family,  e  g.,  Hyacinth,  Narcissus,  etc.).  Iris,  a  Grass  (especially  the  Oat), 
Wandering  Jew,  Anemone,  etc. 


THJi]    WOMK   OF   LEA  VES  197 

dermis  is  then  seen  to  be  made  up  of  a  series  of  cells, 
all  lying  in  one  plane,  with  their  edges  closely  joined 
except  at  certain  points  where  openings  exist  (Figs. 
113  and  114,  s).  Each  opening  (called  a  stoma,  plural 
stomata)  is  surrounded  by  crescent-shaped  cells  called 
the  guard-cells  (r/).  The  openings  are  filled  with  air, 
giving  them  a  dark  appearance.  Compare  the  num- 
ber of  openings  on  the  upper  and  the  lower  surfaces. 
Does  it  correspond  with  what  you  have  already  learned 
by  means  of  the  air-pump! 

Now  let  us  examine  the  interior  of  the  leaf.^  For 
this  purpose  roll  a  leaf  tightly,  hold  the  roll  firmly  be- 
tween the  thumb  and  forefinger  of  the  left  hand,  and 
with  a  sharp  razor,  moistened  in  water,  cut  the  thin- 
nest possible  slices  across  the  leaf;  the  slices  should 
be  so  thin  as  to  appear  almost  or  quite  colorless. 
Transfer  some  of  these  with  a  wet  camel's -hair  brush 
to  a  drop  of  water  on  a  slide,  cover  and  examine  as 
before.  The  epidermis  of  the  upper  surface  (Fig.  113, 
e)  appears  as  a  nearly  colorless  row  of  cells.  The 
function  of  the  epidermis  is  to  protect  the  leaf  from 
drying  up,  as  well  as  against  the  attacks  of  parasites, 
insect  enemies,  etc.  For  this  reason  its  outer  wall 
(cuticle,  Fig.  114,  c)  is  thickened  and  made  water-proof 
(or  almost  so).     Below   the    epidermis    appear   long, 

^  The  leaf  of  the  common  Yellow  Mustard  is  chosen  here  because  it  is  easy 
to  obtain  and  easily  prepared,  while  showing  the  parts  of  the  leaf  with  great 
distinctness:  leaves  of  Beet,  Beech,  etc.,  are  excellent:  any  thin,  tender  leaf 
may  be  used. 


is 


9  £l 
1- 


200  EXPERIMENTS    WITH  PLANTS 

cylindrical  cells,  like  a  lot  of  tubes  standing  on  end, 
closely  packed  together.  These  cells  (p,  called  the  pali- 
sade cells  from  their  resemblance  to  a  palisade)  contain 
a  good  deal  of  leaf -green,  or  chlorophyll,  in  the  form 
of  drops  or  granules  (these  are  called  chlorophyll 
granules,  cliL  gr.)  thickly  scattered  upon  the  inner  sur- 
faces of  the  walls  of  the  cells.  Below  these  is  the 
spongy  tissue  {sp)  ^  composed  of  loosely  joined  cells, 
with  large  air-spaces  between  them.  Under  the  micro- 
scope the  air- bubbles  in  these  spaces  have  a  dark 
appearance.  Finally  comes  the  lower  epidermis,  re- 
sembling the  upper,  but  provided  with  abundant  sto- 
mata,  one  of  which  is  shown  cut  across  at  (s).  Notice 
the  opening  with  the  two  guard-cells,  seen  in  section, 
and,  just  above  the  opening,  a  large  air-chamber  (a) 
which  communicates  with  the  air-spaces  of  the  spongy 
tissue.  The  air,  therefore,  may  penetrate  through  the 
stomata  to  the  interior  of  the  leaf,  where  a  great  ab- 
sorptive surface  (many  times  greater  than  the  external 
surface  of  the  leaf)  is  spread  out.  As  the  cells  of  the 
leaf  are  full  of  liquid,  this  surface  is  constantly  moist, 
and  therefore  in  the  best  condition  for  absorbing 
carbon  dioxide,  just  as  the  moist  surfaces  of  the 
lung-cells  are  in  condition  to  absorb  oxygen.  If  these 
surfaces  should  become  dry  they  would  lose  their 
power  of  absorbing  gases  almost  entirely. 

•  The  leaf  is,  therefore,  an  absorbing  organ,  as  well 
as  the  root:  the  one  absorbs  air- food  (carbon  dioxide), 


THE    WORK   OF  LEAVES  201 

the  other  soil- food  (water  and  the  substances  dissolved 
m  it) .  These  two  kinds  of  raiv^  or  crude  food  meet  in 
the  leaf,  and  there  unite  to  form  elaborated  food, 
i.  e.,  sugars,  starch,  fats,  oils,  proteids,  etc. 

The  leaf  absorbs  not  only  food,  but  energy,  i.  e., 
sunlight,  which  is  needed  to  manufacture  elaborated 
food.  The  absorption  of  light  is  the  work  of  the  green 
coloring  matter,  the  chlorophyll,  and  especially  of  the 
palisade  cells,  which  are  on  the  upper  side  of  the  leaf, 
directly  exposed  to  the  light.  If  we  examine  a  section 
of  a  leaf  which  exposes  both  sides  equally  to  the  light 
(such  as  Iris,  Gladiolus,  etc.),  we  find  palisade  cells 
on  both  surfaces  (Fig.  114) .  In  many  leaves  there  is 
but  a  single  row  of  palisade  cells,  while  in  others  we 
find  a  double  row  (Fig.  113) ,  which  results  in  the  more 
complete  absoi'ption  of  light.  The  ability  of  leaves  to 
absorb  light  is  easily  tested  by  making  a  tube  (about 
an  inch  in  diameter  and  twelve  inches  long)  of  card- 
board, directing  it  toward  the  light,  placing  a  leaf  over 
the  end  and  looking  through  it.  Find  out  how  many 
thicknesses  of  leaf  are  necessary  to 
absorb  the  light  completely. 

Within  the  tiny  chlorophyll  gran- 
ules, the  chlorophyll  is  scattered  in 
the  form  of  very  minute  drops  (Fig.     115.  a  single  ohiorophyii 

grain   containing    very 

115),  which  arrangement  enormously        young  starch-grains  .-it 

^'  "  '^  IS  dotted  to  indicate  the 

increases   the   absorptive   surface  of        phyV  Vs^'disVrfhiued  Tn 

,^^^  in  t  xi'i  the    form  of   very  mi- 

the  chlorophyll,  and  consequently  its        nute  drops. 


202 


EXPERIMENTS    WITH    PLANTS 


^^r  ^^^s"^ 


efficiency.  In  order  to  do  its  Avork  of  starch-making, 
the  chlorophyll  must  absorb  rapidly  large  quantities  of 
carbon  dioxide,  as  well  as  large  amounts  of  energy. 
The  union  of  carbon  dioxide  and  water  under  the 
influence  of  the  absorbed  energy  (sunlight)  produces 
grape-sugar,  which  is  stored  up  in  the  form  of  starch, 
or  else  diffuses  out  into  the  cells  and  thence  to  the 
veins.  The  transfer  to  the  veins  is  greatly  assisted  by 
the  funnel-shaped  collecting  cells  {col.)  and  the  con- 
veying cells  {conv.  Figs.  113  and  114). 

If  we  examine   (with  the  high  power  of  the  micro- 
scope)   a  section  of   a  leaf  which   has   been   removed 

from  the  plant  toward  the  close 
of  the  day,  we  find  the  chloro- 
phyll granules  full  of  small 
white  glistening  bodies  which 
turn  dark  when  we  place  the 
section  in  iodine  solution  (Fig. 
116).  These  are  the  small  grains 
of  starch,  which  have  been 
formed  by  the  union  of  carbon 
dioxide  and  water  under  the  in- 
fluence of  sunlight.  During  the 
night  they  are  again  changed  to 
sugar,  which  travels  along  the 
veins  down  into  the  stem  and  root.  This  movement 
of  sugar  takes  place  during  the  day  also,  but  the 
sugar   is    then    manufactured    faster    than    it    can    be 


116.  A  single  cell  of  a  leaf  with 
chlorophyll  grains  (c/ii.flrr), con- 
taining starch-grains  [st.  gr.) 


THJi]    WONK    OF    LKA  VES 


203 


carried    away,    and    it    is   consequently  stored   up    as 
starch. 

Every  one  has  noticed  that  leaves  removed  from 
the  plant  quickly  dry  up  unless  placed  in  water. 
It  would  seem  that  they  must  lose  water 
rapidly  by  evaporation.  Is  this  normally 
the  case  when  they  are  growing  on  the 
plant?  Obtain  two  watch-crystals  of 
about  the  same  size  (pieces  of  mica 
or  glass  may  be  used  if  the  watch 
crystals  are  not  obtainable) ,  and  fasten 
them  to  opposite  sides  of  a  leaf  by  a 
piece  of  wire  bent  to  form  a  clip,  as 
shown  in  Fig.  117.  Seal  the  joints 
between  the  leaf  and  the  glass  air  -  tight  with  vaseline 
(the  leaf  should  not  be  removed  from  the  plant  and 
care  should  be  taken  not  to  injure  it  in  any  way) .  If 
the  leaf  gives  off  water- vapor,  it  will  condense  in  the 
form  of  drops  inside  the  watch-crystal,  especially  when 
cooled.  Examine  the  leaf  from  time  to  time  and  re- 
move to  a  cool  place  if  necessary.  Do  you  find  that 
the  leaf  gives  off  water  ?  ^  From  which  side  is  more 
given  off  ?    Is  this  the  side  on  which  the  greater  num- 


117.  Arrangement  for 
determining  whether 
a  leaf  gives  off  water 
vapor. 


1  A  more  quick  and  accurate  method  i.s  to  cover  the  leaf  with  paper  im- 
pregnated with  cobalt  chloride  (4  to  5  per  cent  dissolved  in  water);  this  is 
dried  over  a  lamp  until  it  appears  intensely  blue.  It  is  then  placed  on  the  leaf 
and  covered  with  mica  or  glass  held  in  place  by  a  clip,  as  shown  in  Fig.  117. 
If  water-vapor  is  escaping  from  the  leaf  the  paper  quickly  assumes  a  reddish 
tint. 


204  EXPERIMENTS    WITH   PLANTS 

ber  of  stomata  occur  (as  shown  by  the  air-pump  or  by 
microscopical  examination)  ? 

Does  the  water  escape  through  the  openings  only? 
Select  a  plant  in  which  there  are  very  few  stomata,  or 
none,  on  the  upper  surface  of  the  leaf  (many  species 
of  Begonia,  Holly,  Willow,  Poplar,  Lilac,  Tulip  Tree, 
Mahonia,  Oleander,  Scarlet  Eunner,  etc.).  After  mak- 
ing sure,  by  testing  with  the  air-pump  or  by  examina- 
tion with  the  microscope,  that  the  stomata  are  absent 
from  the  upper  surface,  remove  several  leaves  from  the 
plant  and  treat  one  lot  by  covering  both  the  stalk  and 
the  lower  surface  of  the  leaf  with  vaseline  or  grafting- 
wax  ;  treat  another  lot  by  covering  the  stalk  and  the 
upper  surface  of  the  leaf  ;  treat  a  third  lot  by  cover- 
ing the  stalk  and  both  surfaces  of  the  leaf.  Attach  to 
each  leaf  a  stout  piece  of  thread  (of  about  the  same 
weight  in  each  case),  and  weigh  (taking  care  not  to 
rub  off  any  of  the  vaseline  in  the  process) .  Suspend 
the  leaves  by  the  attached  pieces  of  thread,  and  re- 
weigh  from  time  to  time.  Does  it  appear  that  much 
more  water  has  escaped  from  the  under  surface  than 
from  the  upper!  Has  there  been  any  loss  from  the 
leaves  which  were  entirely  covered?  If  so,  it  indicates 
the  amount  of  experimental  error  due  to  the  incomplete 
sealing  with  vaseline,  and  this  should  be  diminished  as 
much  as  possible  by  any  suitable  means.  (It  must  be 
remembered  that  unless  care  is  taken  some  of  the 
vaseline  may  rub  off,  or  in  a  sunny  place  some  may 


THE    WOBK   OF  LEAVES 


205 


melt  and  run  off  if  it  is  too  thickly  smeared  on  ;  for 
this  reason  grafting- wax  is  better.) 

In  examining  the  epidermis  of  leaves  under  the 
microscope,  we  find  the  stomata  sometimes  open  and 
sometimes  closed,  as  in  Fig. 
113.  Since,  as  we  have  already 
found,  all,  or  nearly  all  the 
water  passes  out  through  the 
stomata,  we  may  judge  whether 
they  are  open  or  closed  by  the 
amount  of  water  the  leaf  gives 
off.  This  may  be  measured  by 
the  methods  just  described  or 
by  means  of  the  apparatus 
shown  in  Fig.  119.  A  leaf  is 
removed  from  the  plant  and 
slipped  into  a  cork  borer 
(just  large  enough  to  re- 
ceive it) ,  which  has  been 
previously  forced  through 
a  rubber  stopper,  as 
shown  in  Fig.  118.  On 
withdrawing  the-  cork 
borer,  the  leaf  will  be  found  firmly  fixed  in  the  rubber 
stopper.  In  this  way  a  leaf  or  a  stem  may  be  quickly 
fixed  air-tight  in  such  a  stopper  without  injury.  A 
piece  of  small  glass  tubing,  about  fourteen  inches 
long  (the  smaller  the  bore  the  better) ,  bent  as  shown 


r 


118. 


Method  of  inserting  a  leaf-stalk 
air-tight  in  a  rubber  stopper. 


206 


EXPEBIMENTS    WITH  PLANTS 


in  Fig.  119,  is  now  forced  through  an  opening  in  the 
stopper  and  the  stopper  is  slowly  forced  into  the  neck 
of  the  bottle,  w^hich  is  filled  to  the  brim  with  water. 
Enough  water  will  usually  run  into  the  tube  during  this 
operation  to  fill  it  completely;  should  this  not  happen, 
fill  the  tube  with  water  before  forcing  the  stopper 
into  the  bottle  and  keep  the  water  from  running  out 
of  the  tube  during  the  insertion  by 
stopping  one  end  with  the  finger.  To 
test  whether  the  stopper  is  tight,  dry 
the  joints  and  blow  at  the  free  end  of 

the  tube  to  see 
whether  water 
can  be  forced 
out.  If  the 
joints  are 
tight,  set  the 
apparatus  in 
a  cool,  shady 
place,  and  let 

it  stand  until  a  little  of  the  water  has  been  absorbed 
by  the  leaf  and  a  small  bubble  of  air  (one -fourth  to 
one-half  an  inch  long)  has  been  drawn  into  the  end  of 
the  tube.  When  this  has  occurred,  dip  the  end  of  the 
tube  into  water,  as  shown  in  the  figure,  attach  a 
ruler  to  the  glass  tube  and,  by  means  of  a  watch,  time 
the  progress  of  the  bubble  along  the  tube  (which 
should  rest  in  a  horizontal  position) .    When  the  bub- 


119.  Apparatus  for  measuring 
the  transpiration  of  a  leaf 
and  the  degree  in  which  it 
is  affected  by  sunlight, 
wind,  rolling  the  leaf,  etc. 


THl!J    WORK   OF   LEA  VES  207 

ble  has  passed  into  the  bottle,  admit  another  by  raising 
the  end  of  the  tube  above  the  water  for  a  short  time. 
When  the  rate  of  water  absorption  and  evaporation 
(usually  called  transpiration)  becomes  fairly  constant, 
transfer  the  apparatus  to  the  sunlight  and  take  observa- 
tions (make  the  experiment  also  with  a  leafy  branch). 

If  an  increase  in  the  rate  of  transpiration  occurs 
in  the  sunlight,  it  may  be  attributed  either  to  the 
opening  of  the  stomata  or  to  the  increase  in  trans- 
piration (through  the  already  open,  or  partly  open, 
stomata)  due  to  rise  in  temperature.  In  most  cases 
both  causes  cooperate  to  increase  the  amount  of  tran- 
spiration. We  can  see  why  it  is  of  advantage  to  the 
plant  to  have  the  stomata  open  in  sunlight,  since  it 
is  then  that  starch-making  goes  on,  and  if  the  openings 
of  the  leaf  were  closed  the  absorption  of  carbon  dioxide 
would  be  impossible.  We  can  also  see  why  the  more 
rapid  evaporation  of  water  which  occurs  when  the 
stomata  are  open  may  be  an  advantage,  since  it  leaves 
behind  in  the  leaf  mineral  substances  (just  as'  boil- 
ing water  in  a  tea-kettle  leaves  behind  a  crust  of  lime 
and  other  mineral  substances  which  are  dissolved  in 
the  water)  which,  as  we  have  already  learned,  are  of 
value  to  the  plant. 

The  stomata  usually  close  when  the  supply  of 
water  begins  to  run  low,  and  we  can  readily  see  why 
this  is  advantageous,  since  otherwise  the  leaf  would 
soon  wilt,  and  may  even  do  so  in  spite  of  the  closing 


208 


EXPERIMENTS    WITH   PLANTS 


of  the  stomata,  as  we  may  observe  on  very  hot  days, 
and  especially  in  hot  dry  winds.    Place  the  apparatus 

out  of  doors  in 
the  wind  (the  hot- 
ter and  drier  the 
wind  the  better) , 
and  observe  the 
effect  on  the  rate 
of  evaporation. 

On  the  other 
h  and,  the  sto- 
mata open  as 
soon  as  favorable 
conditions  for 
starch- making  (i. 
e.,  the  requisite 
supply  of  water, 
sunlight  and 
warmth)  return. 
The  plant  has  in  the  stomata  and  guard -cells  an 
automatic  apparatus  of  great  efficiency,  yet  wonder- 
fully simple,  on  whose  proper  working  its  very  life 
depends.  If  we  examine  a  stoma  carefully,  we  see 
the  two  sausage -shaped  guard- cells  filled  with  green 
chlorophyll  granules,  while  the  surrounding  epidermal 
cells  have  none.  It  is  on  this  that  their  opening 
and  closing  depends.  Under  conditions  favorable  for 
starch- making,  the  guard- cells  produce  sugar,  which 


120.  Diagram  showing  in  section  and  surface  view  the 
form  and  position  of  the  guard-cells  when  closed 
(heavy  lines)  and  open  (light  lines). 


THE    WORK   OF  LEAVES 


209 


draws  water  from  the  neighboring  cells  and  causes  the 
guard- cells  to  expand  and  open  the  stomata.  When, 
on  the  other  hand,  unfavorable  conditions  come,  the 
sugar -making  ceases,  and  if  the  water  supply  begins  to 
run  low  the  guard- cells  collapse  and  close  the  stomata. 
The  manner  in  which  the  opening  and  closing  is 
effected  may  be  explained  by  reference  to  Fig.  120, 
which  shows  a  stoma  of  Iris  in  both  the  closed  and 
the  open  position.  The  guard- cell  (as  seen  in  cross- 
section,  Fig.  121)  has  a  thick  wall  on  the  side 
toward  the  stoma  and  a  thin  wall  on  the  opposite  side. 
According  to  mechanical  laws,  when  such  a  structure 
expands  from  internal  pressure  (due  to  the  absorption 
of  water)  the  thinnest  or  weakest  side  must  bulge 
outward,  causing  the  cell  to  curve  (as  shown  by  the 
light  lines  in  Fig.  120) .   When  the  guard-cells  expand, 


121. 


Diagram  of  a  stoma  of  Iris  (seen  in  section)  showing  guard-cells 
and  neighboring  cells  of  epidermis. 


210 


EXPKBIME^TS     WITH    PLA.XTS 


122.  Artificial 
stoma  and 
guard-cells. 


therefore,  they  curve  away  from  each 
other,  leaving  the  stoma  open;  when  they 
collapse  again,  it  closes.  Various  modifica- 
tions of  this  mode  of  action  occur.  The 
general  relations  of  the  guard -cells  and 
surrounding  cells  may  be  seen  in  Fig.  121. 

If  we  tear  off  a  strip  of  epidermis  from 
a  leaf  of  a  Lily  or  Amaryllis  and  mount  it 
on  a  slide  in  water,  we  shall  (if  the  plant 
is  well  supplied  with  water  and  exposed  to 
sunlight)  probably  find  the  stomata  open  : 
if  now,  we  lift  the  cover -glass  and  intro- 
duce a  drop  or  two  of  sugar  or  salt  solu- 
tion, the  water  will  be  withdrawn  from  the 
guard- cells  and  they  will  at  once  collapse 
and  close  the  stomata. 

The  principle  by  which  the  stomata 
open  and  close  may  be  illustrated  by  means 
of  the  model  shown  in  Fig.  122.  A  piece 
of  quarter -inch,  thin -walled,  black  rubber 
tubing,  which  is  not  so  old  as  to  have  lost 
its  elasticity,  is  reinforced  throughout  its 
entire  length,  with  the  exception  of  half  an 
inch  in  the  middle,  by  a  strip  of  elastic 
band  (about  one -eighth  inch  wide)  firmly 
attached  with  rubber  cement.  It  is  then 
bent  in  the  middle,  as  shown  in  the  figure, 
so  as  to  bring  the  reinforced  walls  facing 


THE    WORK   OF   LEA  VES 


211 


each  other,  and  is  secured  at  the  bend  by  a  clothes-pm. 
The  free  ends  are  connected  to  the  arms  of  a  glass 
U-tube  which  have  been  bent  near  together.  The  end 
of  the  U-tube  is  connected  by  a  stout  piece  of  rubber 
tubing  with  a  bicycle  pump.  The  connections  are  all 
tightly  tied  with  twine  or  elastic  bands,  and  air  is 
pumped  in.  As  the  pressure  increases,  the  outer,  thin- 
ner walls  of  the  rubber  guard-cells  bulge  outward, 
causing  them  to  curve  and  leave  the  stoma  or  space 
between  them  ppen  ;  when  the  pressure  is  released 
they  collapse  and  close  it.  The  degree  of 
opening  or  closing  is  great  or  small  accord- 
ing to  the  elasticity  of  the  rubber,  the 
rigidity  of  the  reinforced  wall,  etc. 

If  a  U-tube  is  not  at  hand,  use  in  place 
of  it  two  short  glass  tubes  inserted  in  a 
rubber  stopper  (enlarged  a  little  at  the  end 
to  prevent  them  from  slipping  out),  as 
shown  in  Fig.  123;  the  cork  is  inserted  in 
a  piece  of  glass  tubing,  at  the  other  end 
of  which  is  a  similar  cork  pierced  with  a 
glass  tube  which  is  connected  with  the 
pump.  A  wire  may  be  passed  over  both 
stoppers    to    hold    them    firmly    in    place* 

The  danger  of  drying  up  is  the  most  serious  with 
which  the  plant  has  to  contend,  and  nothing  affects 
the  health  of  a  plant  so  quickly  as  lack  of  water. 

Plants  suffering  from  dryness  show  very  character- 


nn 


ijl 


/\ 


123.  Modifica- 
tion of  part 
of  the  appara- 
tus shown  in 
Fig.  122. 


212  EXPERIMENTS    WITH   PLANTS 

istic  symptoms  i.  e.,  wilting,  drooping  and  yellowing  of 
the  leaves,  followed  in  time  by  the  fall  of  the  leaves, 
beginning  usually  with  the  oldest.  In  regard  to  the 
cause  of  the  falling  of  leaves  in  autumn,  see  page  332. 
It  is  interesting  to  note  that  when  the  leaves  fall  away 
they  leave  a  smooth  scar ;  this  is  due  to  the  formation 
of  a  layer  of  loose  cells  just  at  the  base  of  the  stalk  (as 
may  be  easily  seen  in  a  section  under  the  microscope) . 
If  leaves  of  the  Kentucky  Coffee  Tree,  Tree  of  Heaven 
(Ailanthus),  Walnut  or  Ash  are  wrapped  in  a  moist 
cloth  and  placed  in  the  dark,  this  layer  forms  very 
rapidly  (in  the  Coffee  Tree  within  forty- eight  hours), 
with  the  result  that  the  leaflets  fall  off,  leaving  a 
clean  scar.  Is  such  a  scar  formed  in  most  monocotyle- 
donous  plants,  such  as  Corn,  Grasses,  Lily,  etc.? 

Plants  which  are  suffering  from  drought  should  be 
watered,  set  in  a  cool,  moist  place  and  sprinkled  with 
water.  If  the  plant  has  suffered  severely  it  may  be 
necessary  to  remove  some  o\  the  older  leaves.  Cut- 
flowers  which  have  wilted  may  be  placed  in  water  and 
covered  with  a  wet  towel,  when  they  will  quickly 
revive. 

Leaves  have  various  devices  to  protect  themselves 
against  the  wilting  due  to  heat  and  dryness.  (What 
leaves  remain  fresh  longest  when  removed  from  the 
plant  for  purposes  of  decoration?  Why?)  Some 
of  these  are  obvious,  and  we  may  test  them  by 
means  of   the  apparatus  shown  in  Fig.  119.    Roll  the 


THE    WORK   OF   LEA  VES  213 

leaf  or  fold  it  two  or  three  times,  after  the  fashion  of 
a  fan,  and  secure  it  by  a  rubber  band.  How  does  this 
affect  the  rate  of  transpiration  ?  Do  you  find  devices  of 
this  kind  among  plants?  Many  Grasses  (e.  g..  Corn)  roll 
up  their  leaves  in  the  heat  of  the  day  or  fold  the 
stomatic  surfaces  together  so  as  to  diminish  transpi- 
ration. Young  leaves  are  far  more  easily  injured  by 
drying  agencies  than  old ;  they  are  nearly  always  rolled 
or  folded  (as  they  issue  from  the  bud)  in  a  manner 
that  greatly  reduces  evaporation,  and  it  will  be  noted 
that  if  one  surface  is  more  exposed  than  another  it  is 
the  stomatic  surface  which  is  protected.  Make  obser- 
vations on  this  point:  study  especially  the  Tulip  Tree, 
Canna,  fruit  trees,  Maple,  Ferns,  etc.  (see  Gray's  Les- 
sons, under  vernation  or  aestivation).  Many  leaves  are 
permanently  rolled  (Heath  plants,  etc.). 

Again,  we  may  cover  the  leaf  in  our  apparatus  with 
cotton  wool,  pressed  down  tightly  against  the  leaf  by 
means  of  wire  netting  laid  over  it  and  held  in  place  by 
clothes-pins.  We  may  cover  both  sides  of  the  leaf  or 
the  stomatic  surface  only,  and  may  note  the  rate  of 
evaporation  in  both  sunlight  and  shade.  Do  you  find 
coverings  analogous  to  this  on  leaves?  Study  the  leaves 
of  the  Dusty  Miller,  Horehound,  Sage,  Wormwood, 
Mullein,  Cinquefoil,  etc.  Many  leaves  have  a  hairy 
covering  during  their  youthful,  sensitive  period,  but 
lose  it  as  they  grow  older  (Horse-chestnut,  Beech, 
Service -berry.  White  Poplar,  Pear,  etc.). 


214  EXPERIMJ^NTS    WITH  PLANTS 

We  have  already  learned  how  a  coat  of  vaseline 
stops  evaporation  from  the  leaf.  Do  you  find  leaves 
coated  with  water-proof  substances,  such  as  resins,  gums, 
varnishes,  wax,  etc.?  Notice  especially  the  varnishes, 
gums,  etc.,  on  buds,  which  prevent  them  from  drying 
up.  Remove  the  scales,  which  are  covered  with  var- 
nish, and  note  the  result.  Many  leaves  have  a  coat  of 
varnish  during  their  youthful  period  but  dispense  with 
it  as  they  grow  older  and  less  sensitive,  and  the  epi- 
dermis thickens  (Cherry,  Poplar,  Birch,  Alder,  Peach, 
etc.). 

Take  two  leaves  of  the  same  size  which  are  thickly 
coated  with  wax  (the  young  horizontal  leaves  of  Euca- 
lyptus are  especially  good) ;  remove  the  wax  fron  one 
by  rubbing  with  a  soft  cloth ;  seal  the  cut  surfaces  with 
vaseline,  place  a  leaf  in  each  pan  of  the  balance,  and 
balance  them  by  adding  weights  to  the  proper  pan. 
Observe  from  time  to  time  which  is  losing  water  more 
rapidly,  as  indicated  by  the  rising  of  the  pan. 

It  will  be  noticed  that  leaves  (Iris,  Bamboo,  Dusty 
Miller,  Oxalis,  Silver-leaved  Poplar,  Blackberry,  etc.) 
which  have  a  covering  of  hairs,  wax,  etc.,  have  a  glis- 
tening silvery  appearance  under  water ;  this  is  due  to  a 
layer  of  air  which  is  held  tenaciously.  On  dipping  such 
leaves  in  water  we  find  that  the  stomatic  surface  is  so 
protected  that  it  does  not  become  wet;  this  is  an  advan- 
tage, since,  if  water  penetrated  into  the  stomata,  it 
would  completely  prevent  the  passage  of  air  and  the 


THE    WORK  OF  LEAVES  215 

absorption  of  carbon  dioxide.  One  of  the  great  dan- 
gers to  plants  in  the  neighborhood  of  factories,  etc., 
is  the  choking  of  the  stomata  with  soot  a,nd  dust. 
Wherever  there  is  much  fine  dust,  plants  suffer  in  this 
respect  unless  frequently  washed  by  rain.^  House - 
plants  are  much  benefitted  by  an  occasional  washing  of 
the  leaves  with  water. 

We  can  readily  understand  that  it  is  an  advantage 
to  have  the  stomata  placed  on  the  under  side  of  the 
leaf,  since  they  are  then  better  protected  against  dust, 
rain,  direct  exposure  to  the  sun,  etc.,  and  this  is  the 
position  in  which  they  principally  occur. 

Other  devices  for  reducing  evaporation  that  may  be 
studied  are  the  sinking  of  the  stomata  in  pits  (Olean- 
der) or  channels  (Cytisus,  Broom,  etc.),  the  reduction 
in  the  number  of  the  stomata  (universal  in  plants 
growing  in  dry  situations),  the  reduction  of  leaf  sur- 
face (in  succulents,  such  as  Hen -and -chickens.  Live- 
forever,  Ice  Plant,  etc.),  dispensing  with  the  leaves 
during  a  portion  of  the  year  (some  Switch  Plants),  or 
complete  and  permanent  loss  of  leaves  (Cacti) .  Obtain 
any  leaves  you  can  of  these  kinds,  and  test  the  amount 
of  evaporation  which  goes  on  in  them.   For  this  purpose 

1  Plants  are  sometimes  injured  when  sprayed  with  oily  liquids  (to  de- 
stroy insect  pests),  by  the  clogging  of  the  stomata  with  oil.  The  result  is  that 
the  leaves  turn  yellow  and  begin  to  drop  off  soon  after  the  spraying  occurs. 

The  fumigation  of  plants  with  poisonous  gases  (to  destroy  insects)  must 
be  carried  on  at  night  when  the  stomata  are  closed.  Otherwise  the  plant  is 
killed. 


216  EXPERIMENTS    WITH  PLANTS 

remove  the  leaf,  weigh,  seal  the  cut  surface  with  vase- 
line or  grafting  wax  and  reweigh;  expose  the  various 
leaves  simultaneously  to  the  same  conditions  for  the 
same  length  of  time  (five  or  six  hours  in  sunshine), 
and  weigh  again;  divide  the  loss  in  weight  (i.  e.,  the 
difference  between  the  results  of  the  second  and  third 
weighings)  by  the  original  weight  (results  of  the  first 
weighing)  to  get  the  percentage  of  loss.  Compare  the 
percentages  for  the  different  leaves  (e.  g.,  a  leaf  of 
Squash  with  that  of  Hen -and -chickens). 

Plants  which  have  adapted  themselves  to  dry  situ- 
ations have,  as  we  have  seen,  a  surprising  ability  to 
retain  water.  In  all  of  the  thick -leaved,  fleshy  plants, 
the  so-called  succulents,  sufficient  water  is  stored  up 
in  reservoirs  (consisting  of  spongy  colorless  tissue)  in 
the  interior  of  the  leaf  to  last  from  one  season  of  rain 
to  another,  often  for  a  period  of  months.  Such  is  the 
case  with  the  Hen -and -chickens.  Live-forever,  Ice 
Plant,  etc.  In  many  of  these,  gummy,  mucilaginous 
substances  or  hygroscopic  salts  are  present  which  hold 
the  water  tenaciously.  Try  the  experiment  of  exposing 
on  a  piece  of  glass  drops  of  pure  water,  together  with 
drops  of  fluid  expressed  from  such  leaves  or  drops  of  a 
strong  solution  of  salt,  sugar  or  gum  arable.  Which 
is  the  first  to  completely  evaporate? 

Along  with  modifications  in  structure  go  changes  of 
position  (e.  g.,  from  horizontal  to  vertical)  which  di- 
minish evaporation.    Notice  the  vertically  placed  leaves 


TEE   WORK  OF  LEAVES  217 

of  Iris,  Gladiolus,  Eucalyptus,  Acacia,  etc.  Observe 
the  behavior  of  Grasses  in  this  respect.  Many  young 
leaves  remain  vertical  until  their  epidermis  becomes 
thick  enough  to  prevent  evaporation,  when  they 
change  to  the  horizontal  position.  Note  as  mciny  cases 
of  this  as  you  can.  Many  adult  leaves  change  their 
horizontal  position  to  the  vertical  one  in  the  middle  of 
hot  summer  days,  when  the  light  and  heat  are  too  in- 
tense. Study  the  familiar  plants  about  you  and  find  as 
many  cases  of  this  sort  as  you  can. 

We  have  already  learned  (page  124)  that  plants 
may  have  their  roots  submerged  in  water  and  yet  suf- 
fer from  lack  of  it.  This  is  because  there  are  sub- 
stances in  the  water  which  attract  it  away  from  the 
plant.  Try  the  experiment  of  placing  leaves  (or  whole 
plants)  with  their  stalks  dipping  in  strong  salt  solu- 
tion. Plants  in  alkali  lr.nds  and  along  the  seashore, 
where  the  water  is  brackish,  suffer  in  this  respect  and 
consequently  show  the  same  devices  to  diminish  evapo- 
ration as  we  find  in  plants  of  desert  or  semi- arid 
regions. 

While  it  is  an  advantage  to  have  the  leaf  placed 
vertically  when  the  sun's  rays  pour  straight  down, 
making  the  light  and  heat  excessive,  it  will,  under 
ordinary  circumstances,  be  far  better  to  have  the  leaf 
placed  at  right  angles  to  the  light,  since  in  this  posi- 
tion the  leaf  can  absorb  the  maximum  amount.  The 
same   leaves  which   in   the  excessive  heat  of  midday 


218 


EXPERIMEXTS     WITH    PLANTS 


place  themselves  vertically  (i.  e.,  parallel  to  the  light) 
will  be  found  in  the  morning  and  afternoon  with  their 
faces  perpendicular  to  the  light;  in  this  way  they  fol- 
low the  sun  all  day,  facing 
eastward  in  the  morning  and 
westward  in  the  afternoon 
(plants  of  the  Pea  family, 
some  Mallows,  etc.) .  What 
common  plants  do  this? 
Study  Clovers,  Lupins, 
Melilotus,  etc.  Notice  the 
cushion  -  like  joints,  or 
hinges,  on  which  the  leaves 

124.    Acacia  leaf,  night  or  sleep  position.       tum. 

Study  the  "sleep -position"  of  leaves  at  night  in 
Oxalis,  Clover,  Acacia  (Figs.  124  and  125),  also  in 
seed-leaves  of  Sunflower,  Squash,  etc.  This  position 
may  be  of  advantage 
in  reducing  evapora- 
tion or  in  diminish- 
ing the  loss  of  heat,  or 
both.  It  may  in  many 
cases  be  produced 
artificially  by  putting 
the  plants  in  dark- 
ness for  a  time  dur- 
ing the  day  (Oxalis, 
Acacia,  Clover,  etc). 


■^:^^' 


X2b.    Acacia  leaf,  clay  position. 


THE     WORK    OF   LEA  VES 


219 


The  ability  to  turn 
toward  the  light  must 
be  extremely  useful. 
Do  all  leaves  have 
this  power?  Experi- 
ment with  as  many 
plants  as  you  can, 
placing  them  before  a 

window,       or      shading  126.     Leaf  mosaic  of  ivy  Geranium. 

them  on  one  side  as  they  grow  out-of-doors.  Notice 
any  cases  where  the  plants  grow  near  walls  or  are  for 
any  reason  shaded  on  one  side.  Study  especially  climb- 
ing vines,  like  the  En- 
glish Ivy,  Boston  Ivy, 
etc.  Do  the  leaves  in 
these  plants  seem  to 
avoid  shading  each 
other?  How  do  you 
explain  this?  When 
leaves  cover  over  the 
available  space  so  as 
to  catch  all  of  the 
light  without  interfer- 
ing with  each  other, 
their  appearance  sug- 
gests a  mosaic  (Figs. 
126  and  127),  and  is 

127.     Leaf-mosaic  of  Chestnut.  Called     a    leai-mOSaiC. 


220 


EXPERIMENTS    WITH   PLANTS 


^^^^pp'  What   are  the  most  perfect  leaf- 

igt^T^  mosaics  you  can  find? 

Notice  the  difference  between 
the  arrangement  of  leaves  on  hori- 
zontal and  vertical  shoots  of  the 
same  plants  (see  Figs.  128,  129  and 
130).  Which  arrangement  re- 
quires the  greatest  bending  and 
twisting  of  the  leaves  out  of  their 
original  position? 

In  what  part  of  the  leaf  is  the 
mechanism  located  by  which  these 
bending  and  twisting  movements 
are  accomplished?  Study  espe- 
cially in  this  respect  the  leaves 
of  the  Scarlet  Eunner  or  other 
bean,  and  examine  the  cushion- 
like swelling  at  the  base  of  the  stalk  of  each  leaf  and 
leaflet. 

Inasmuch  as  a  tree  forms  its  branches  and  leaves 
with  reference  to  the  light,  prevail- 
ing winds,  etc.,  it  follows  that  when 
it  is  transplanted  its  orientation 
should  not  be  changed,  i.  e.,  the 
same  side  should  be  toward  the  north 
both  before  and  after  planting. 

129.     Appearance    of    the 

Study  both  trees  and  shrubs  (the        branch  shown  in  rig. 

n  ■,         .  n\xT  128   when   viewed  from 

smaller  plants  as  well),  to  discover        above. 


128.    Upright  branch  of  Peri 
winkle  ( Vinca). 


THE    WOBK   OF  LEAVES 


221 


on  which  side  their  greatest  development  occurs  and 
how  this  is  affected  by  light. 

The  leaf,   more  than  any  other  part  of  the  plant, 
needs   protection 
against     animals,     ^^ 
insects   and  para-  ^ 

sites.  Devices  for 
this  purpose  are 
found  in  great 
variety.  Make  a 
practical  study  of 
the  following 
forms  of  protec- 
tion. 

( a )  Prickles, 
spines,  thorns, 
hairs,  etc.  These 
protective  weap- 
ons are  borne  by 
both  leaf  and 
stem,  and  may  be  outgrowths 
from  the  surface  (prickles  of 
Rose  and  Thistle,  stinging  hairs 
of  Nettle,  which  break  off  in 
the  wound  and  discharge  an  irritating  poison  into  it, 
hairs  of  Mullein,  which  are  irritating  to  the  mouth, 
etc.),  or  the  spiny  tip  of  the  leaf  (Thistle,  Spanish 
Bayonet,  etc.),  or  th6  teeth  of  the    edge   of   the   leaf 


KiO.  Horizontal  (trail- 
ing) branch  from  the 
same  plant  from 
■which  the  upright 
branch  shown  in  Figs. 
128  and  129  was  taken. 


222  EXPERIMENTS    WITH   PLANTS 

(Sedges,  Grasses,  Holly,  Century  Plant),  or  the  stip- 
ules of  the  leaf  modified  into  thorns  (Locust),  or  the 
whole  transformed  leaf  (Barberry),  or  a  transformed 
branch  (Hawthorn,  Honey  Locust). 

{h)  Bitter  or  poisonous  substances.  It  would  be 
very  interesting  to  know  how  animals,  both  wild  and 
domestic,  learn  to  avoid  poisonous  plants.  Many 
plants  have  a  disagreeable  or  offensive  odor  which 
warns  them  away,  as  the  Jimson  Weed  or  Thorn  Apple, 
and  many  others.  Many  have  a  disagreeable  taste, 
e.  g..  Poppies. 

But  there  are  many  others  which  to  us  have  neither 
disagreeable  taste  nor  odor,  and  yet  are  avoided  by 
grazing  animals  of  all  kinds.  In  this  respect  their  in- 
stincts are  superior  to  ours.  There  are  some  poisonous 
plants,  notably  the  "loco  weeds,"  which  are  eaten  by 
domestic  animals  and  which  produce  dizziness,  vertigo 
and  insanity.  It  is  stated  on  good  authority  that  the 
loco  habit  may  be  taught  by  a  single  animal  to  a 
whole  herd,  and  that  an  animal  which  has  been  appar- 
ently cured  of  the  habit  by  treatment  is  never  entirely 
trustworthy  thereafter.^ 

In  general,  however,  poisonous  plants  are  avoided, 
and  the  same  is  true  of  many  plants  which  are  bitter  or 
disagreeable    without   being   poisonous   (e.  g.,  Worm- 

'  The  annual  loss  from  poisonous  plants  on  the  western  stock  ranges  is 
aVjout  $400,000.  See  the  article  by  Chestnut,  in  the  Year  Book  of  the  U.  S. 
Department  of  Agriculture  for  1900. 


TEE    WO  UK   OF   LEAVES  223 

wood,  Ragweed,  Boueset,  etc.).  There  can,  therefore, 
be  no  doubt  of  the  efficiency  of  this  kind  of  protection. 

(c)  Woody,  leatliery  texture,  as  in  Rushes  (or  flinty, 
as  in  Horse-tails) ,  is  a  means  of  protecting  many  plants, 
a  fact  which  is  familiar  to  all. 

{d)  Hugging  the  ground  is  a  very  successful  device 
employed  by  plants,  such  as  Knot-grass,  Cinquefoil, 
Purslane  ("Pusley"),  Wild  Strawberry,  etc. 


CHAPTER   V 


THE  WORK  OF   STEMS 


The  work  of  the  stem  and  the  work  of  the  leaf  are 
closely  connected.  We  have  learned  that  the  leaf 
needs  a  constant  supply  of  water;  this  is  absorbed  by 
the  root,  but  in  order  to  reach  the  leaves  it  must  be 
conveyed  upward  through  the  stem.  Where  does  the 
water  travel  in  the  stem?  Cut  olf  a  leafy  branch  (pref- 
erably of  Squash,  Sunflower  or  Geranium),  and  place 
the  cut  end  in  water  in  which  enough  eosin  has 
been  dissolved  to  give  it  a  bright  red  color.  Place  it 
where  the  conditions  are  favorable  for  evaporation,  and 

in  an  hour  or  so  cut  off  the 
stem  two  or  three  inches 
from  the  lower  end;  if  the 
liquid  has  risen  in  the  stem 
trace  it  upward  by  means  of 
successive  cuts.  Make  a  dia- 
gram showing  the  portion  of 
the  stem  in  which  the  colored 
liquid  rises.  If  a  Squash 
stem  be  used,  the  appearance 
when    cut   across   resembles 

(224) 


131.  Diagram  of  cross-section  of  Squash 
stem:   {str)  strengthening  fibers. 


I 


THE    WORK  OF   STEMS  225 

Fig.  131  in  the  essential  points.  In  each  of  the  angles 
of  the  stem  is  a  large,  fibrous  bundle  or  strand;  alter- 
nating with  these  are  five  bundles  toward  the  center  of 
the  stem.  The  central  portion  of  each  bundle  (the 
wood)  is  colored  red  by  the  fluid;  on  each  side  of  the 
wood  is  a  mass  of  softer  tissue  somewhat  translucent 
(the  soft  bast),  from  the  cut  surfaces  of  which  issue 
mucilaginous  drops. 

Allow  the  branch  to  stand  in  the  solution  until  the 
leaves  become  colored  red,  and  then  cut  the  stems 
lengthwise  and  trace  the  course  of  the 
bundles  up  through  it  and  out  into  the 
leaves.  Hold  the  leaf  up  to  the  light 
and  notice  the  brauching  of  the  bun- 
dles, or  veins.  Use  a  lens  to  follow  the 
finer  branches.  Place  a  very  young 
leaf,  not  over  a  quarter  of  an  inch  long,     ^^^-  ^""^  '^^^^  '^°'^: 

'  ^  ^ '  ing  arrangement  of 

on  a  glass  slide  in  a  drop  of  alcohol  to  fi^^^o^s  bundles. 
which  lye  has  been  added,  and  allow  it  to  bleach;  rinse 
with  water,  mount  on  a  slide  in  water,  examine  with 
the  microscope  and  try  to  find  the  ends  of  the  veins. 
Trace  the  bundles  down  into  the  root.  Pull  up  some 
vigorous  plants  by  the  roots,  cut  off  the  ends  of  the 
roots,  place  the  plants  in  eosin  solution,  and  follow  the 
path  of  the  solution  into  the  root  and  up  into  the  stem. 
Make  a  diagram  of  the  path  of  the  solution  in  the  root 
(see  Fig.  90).  Examine  the  Corn  (Fig.  132),  tracing 
the  bundles   up  through  the    stem   and  out   into   the 

o 


226  EXPEBIMENTS    WITH   PLANTS 

leaves*  Bundles  which  group  themselves  into  a  circle 
in  the  stem  and  form  a  branching  network  in  the 
leaves,  as  in  the  Squash,  are  characteristic  of  a 
great  group  of  plants,  the  Dicotyledons  (plants  with 
two  seed-leaves) ;  a  scattered  arrangement  of  bundles 
in  the  stem,  together  with  a  parallel  course  in  the 
leaves,  as  seen  in  the  Corn,  is  characteristic  of  the 
great  group  of  Monocotyledons  (plants  with  one 
seed-leaf) . 

Place  a  small  leafy  branch  of  Oak,  Hickory  or 
some  other  hard  wood  in  the  solution,  and  follow  the 
path  of  the  liquid  to  the  very  extremity  of  the  growing 
tip.  At  the  very  tip  the  wood  is  in  separate  bundles, 
as  in  the  Squash,  but  as  we  follow  it  down  toward  the 
older  part  of  the  stem  the  separate  bundles  very  soon 
coalesce  to  form  a  continuous  ring  of  wood  (and  also 
of  bast) . 

Take  one  of  the  Squash  vines  which  has  stood  in 
the  solution  for  some  time,  cut  it  square  across,  and 
from  the  cut  surface  take  (with  a  sharp  razor)  sections 
(thin  enough  to  be  translucent  but  still  fairly  thick), 
and  place  them  (without  water  or  cover -glass)  on  a 
slide,  and  examine  with  the  low  power  of  the  micro- 
scope. The  fibrous  bundles  show  the  wood  (i.  e.,  the 
central  portion  of  each  bundle)  colored  red,  with  the 
uncolored  bast  lying  on  either  side  of  it.  Turning  our 
attention  to  the  wood,  we  see  in  it  two  large  openings, 
the  ducts  (see  Fig.  133).    In  tracing  the  colored  fluid 


C/?  OSS 


S  £-  C  T / OA/ 


f^a/ndium 


uccd 


bast 

*/> 
bast 
LONGfTUDi NAL  S £ C  T / O /V 

133.     Stem  of  8quu«h:   (rf)  duct,  (*rp)  wood    pH.-eiichvTna.  (ir)  trHcheid.  (.*0  sieve-tube 
{sp)  sieve-plate.  Uc)  comDanion  eeU,  {hp)  bast  parenchyma. 


228  EXPERIMENTS    WITH  PLANTS 

up  the  stem,  we  notice  that  it  travels  much  faster  in 
these  ducts  than  in  the  other  parts  of  the  wood. 
Between  the  ducts  is  a  mass  of  smaller  cells,  which 
also  become  colored  by  the  liquid  after  a  time  and 
which  appear  therefore  to  assist  in  conveying  water. 

Having  made  out  these  points,  we  may  take  from 
the  cut  surface  of  the  stem,  by  means  of  a  razor 
moistened  in  water,  the  thinnest  possible  slices  (when 
thin  enough  they  are  almost  colorless  and  will  sink  in 
water ;  in  this  way  they  may  be  separated  from  the 
thicker  ones).  Transfer  them  (by  means  of  a  camel's- 
hair  brush  dipped  in  water  or  the  point  of  a  knife)  to 
a  glass  slide,  and  cover  with  a  cover-glass.  Examine 
first  with  the  low  and  then  with  the  high  power  of  the 
compound  microscope. 

Let  us  now  cut  the  stem  lengthwise  in  such  a  way 
as  to  divide  a  bundle  lengthwise  into  two  halves  in  a 
plane  passing  through  the  center  of  the  stem.  From 
one  of  the  cut  surfaces  take  sections  (thin  enough  to 
be  translucent),  place  them  (without  water  or  cover- 
glass)  on  a  slide,  and  examine  with  the  low  power. 
We  now  see  that  the  bundle  consists  of  a  mass  of  elon- 
gated tubes  packed  closely  together,  the  central  portion 
of  which,  the  wood,  is  conspicuous  by  the  red  colora- 
tion due  to  the  eosin  ;  the  ducts  are  very  conspicuous 
by  reason  of  their  large  size. 

Let  us  now  cut  much  thinner  sections  from  a  cut 
surface  prepared   in  the  same  way,   mount   them  in 


I 


TEE    WOBK  OF   STEMS  229 

water  under  a  cover- glass  and  examine  with  the  high 
power.  We  see  that  both  the  ducts  (d,  Fig.  133)  and 
some  of  the  smaller  cells  of  the  wood  are  covered  with 
regular  markings,  round  or  elliptical  in  shape  ;  these 
are  thin  places  in  the  walls  called  pits  (jo,  Fig.  138) 
through  which  water  may  pass  readily  from  one  cell 
to  another.  The  smaller  cells  of  the  wood  are  of  two 
kinds  ;  short  cells  with  blunt  ends  (called  wood  paren- 
chyma, wp) ,  and  longer  cells  with  pointed  ends  (called 
tracheids,  tr) ;  these  latter  have  thin  walls  with  spiral 
or  annular  (i.e.,  ring-shaped)  thickenings.  The  spiral 
and  annular  thickenings  of  the  cell- wall  are  exceedingly 
useful  to  prevent  the  cells  from  being  crushed  by  the 
pressure  of  the  surrounding  cells  and  so  rendered  use- 
less for  the  conveyance  of  water.  As  we  follow  the 
bundles  up  into  the  tip  of  the  stem,  we  notice  that 
the  spiral  and  annular  tracheids  are  the  first  elements 
of  the  wood  to  be  formed,  and  that  their  structure 
allows  them  to  stretch  so  as  to  keep  pace  with  the 
growth  in  the  length  of  the  stem,  since  they  are 
formed  in  the  growing  region  of  the  stem  near  the  tip. 
The  thick-walled  elements  of  the  wood  can  stretch 
little  or  not  at  all,  and  they  acquire  their  thick  walls 
(and  characteristic  structure)  in  the  region  just  below 
the  growing  portion  of  the  stem  where  elongation  has 
practically  ceased  (see  page  249). 

Can  you  explain  why  the  water  rises  so  much  more 
rapidly  in  the  ducts  than  in  the  other  cells  ?    Not  only 


230  EXPEKIMEXTS     WITH    PLANTS 

are  they  larger,  but  the  water  meets  with  no  obstruc- 
tions ill  passing  through  them,  while  in  the  smaller 
cells  there  are  cross-walls  at  frequent  intervals  through 
which  it  must  pass.  Such  cross -walls  occur  also  in 
the  ducts  at  an  early  stage  of  their  development,  but 
they  are  soon  broken  down  and  absorbed,  and  we  find 
only  remnants  of  them  in  the  form  of  rings  here  and 
there  on  the  walls  of  the  ducts  (as  shown  in  Fig. 
133). 

On  comparing  a  fibrous  bundle  of  the  Corn  (Fig. 
134)  with  that  of  the  Squash,  we  find  also  two  large 
ducts  {d,  d) ,  together  with  (usually)  an  annular  tra- 
cheid  (a)  and  a  spiral  one  {sp),  beside  which  is  a  large 
air-space,  the  effect  of  a  tear  in  the  tissues  caused  by 
rapid  growth;  the  rest  of  the  wood  consists  of  wood 
parenchyma   {ivp) . 

Let  us  now  investigate  the  wood  of  an  Oak  (or 
other  hardwood  tree  such  as  Hickory,  Chestnut,  Ash, 
Acacia,  etc.)  and  of  a  Pine  (or  other  softwood  tree 
such  as  Spruce,  Cypress,  Juniper,  etc.)  by  first 
tracing  the  path  of  the  water  (by  means  of  eosin 
solution)  and  then  examining  sections  under  the  micro- 
scope. Cutting  sections  of  woody  stems  presents 
certain  mechanical  difficulties,  but  these  are  easily 
overcome  if  we  choose  young  stems  (not  more  than 
two  or  three  years  old)  and  trim  the  surface  to  be 
cut  until  it  is  not  more  than  an  eighth  of  an  inch  in 
diameter. 


I 


cri/shed 
bast 


134.  Cross-section  of  a  bundle  of  Corn:  (d)  duct,  (a)  annular  tracheid  (i.  e..  with  ring- 
shaped  thickenings),  {sp)  spiral  tracheid  (i.  e.  with  spiral  thickenings),  {wp)  wood 
parenchyma,  {si)  sieve-tube,  {cc)  companion  cell,  {sir)  strengthening  fibers. 


sscr  /oAf 

,       .  rind  (of  ccffex) 


€or.  fi-^-'^^et^cc*!!^ 


rind  (tr  cortex) 
LONCtT  UDI NAL     ^£CT/ON 

135.  Oak  branch:  (cA;)  cork,  ice")  cork  cambium,  {coV)  collenchyma,  ^cor.v)  cortical 
parenchyma,  {sir)  strengthening  cells,  {cr)  crystal-bearing  cells,  (6j))  bast  paren- 
chyma, {sp)  sieve -plate,  (sO  sieve -tube,  (d)  duct,  {tr)  tracheid,  Kxvp)  wood 
parenchyma,  {st.  wp)  wood  parenchyma  containing  starch,  {mr)  medullary  ray, 
{I)  lenticel. 


THE    WORK  OF  STEMS  233 

In  the  wood  of  the  Oak  (Fig.  135)  we  find  the  same 
elements  as  in  the  Squash,  namely,  ducts  (o?),  wood 
parenchyma  {wp)  ^  and  long,  pointed  tracheids  (^r), 
dovetailed  together  at  the  ends.  Most  of  the  tracheids 
in  the  Oak  are  pitted;  tracheids  with  spiral  or  ring- 
shaped  thickenings  occur  only  in  the  innermost  wood 
next  to  the  pith.  The  wood  parenchyma  cells  are 
usually  distinguished  by  being  filled  with  starch,  so 
that  by  placing  the  section  in  iodine  they  stand  out 
prominently;  at  the  same  time  the  medullary  rays 
(mr),  or  silver  grain  of  the  wood,  stand  out  unmis- 
takably by  reason  of  their  starch -content.  Whether 
we  look  at  the  cross  or  the  longitudinal  section,  the 
starch,  by  its  dark  coloration,  forms  a  distinct  pattern, 
which  shows  very  clearly  the  course  it  travels  from  the 
outer  green- celled  tissue  of  the  rind,  inward  through 
the  narrow,  ribbon-like  medullary  rays,  and  from 
them  into  the  intersecting  bands  of  wood  parenchyma 
in  which  it  travels  freely  up  and  down  the  stem. 
The  form  of  the  medullary  rays  (mr)  is  easily  under- 
stood from  the  figure.  They  consist  of  cells  elongated 
in  the  direction  of  the  radius  of  the  stem,  and  run  from 
the  rind  (or  cortex)  through  the  bast  into  the  wood, 
many  of  them  reaching  clear  to  the  pith,  to  which 
they  convey  large  quantities  of  starch.  In  the  longi- 
tudinal section  the  cells  of  medullary  rays  are  shown  in 
surface  view  (i.  e.,  not  cut  open),  consequently  we  see 
the  pits  which  occur  in  their  walls;  it  is  principally 


234 


EXPERIMENTS    WITH  PLANTS 


through  these   pits   (which   are   openings   in  the  wall 
closed  by  very  delicate  membranes)   that  the   starch 

passes  in  the 
form  of  dis- 
solved grape- 
sugar  from 
cell  to  cell. 
These  pits 
occur  on  all 
the  cell-walls 

186.     Bordered  pit,  cut  in  lialf  (diagrammatic).  of     thc     WOOd 

and  are  shown  in  the  cross -section  as  dots  in  the  cell- 
wall  (for  details  see  Fig.  136,  which  is  a  diagrammatic 
representation  of  one  of  these  bordered  pits  cut  through 
the  center;  a  similar  section  of  a  simple  pit  is  shown 
in  Fig.  137) .  These  figures  make  it  clear  that  the  pits 
are  nothing  more  than  holes  in  the  wall  across  which 
are  stretched  delicate  membranes  which  allow  water  to 
pass  through  but  prevent  the  passage  of  air- bubbles, 
starch  grains,  etc.  On 
looking  at  a  bordered  pit, 
the  narrowed  entrance  to 
the  hole  appears  as  a 
smaller  circle  within  the 
larger  one  which  corres- 
ponds to  the  diameter  of 
the  hole  at  its  widest 
part.    It  is  possible  that 


137.     Simple  pit,  cut  iu  half  (diagrammatic] 


THE    WORK  OF    STEMS  235 

air- bubbles,  which  would  hinder  the  rise  of  the  water, 
are  trapped  in  these  pits  and  so  rendered  harmless. 
The  tracheids  and  wood  parenchyma  are  also  pitted  so 
as  to  allow  water  and  dissolved  substances  to  pass 
readily  from  one  to  another.  The  great  elongation  of 
the  tracheids  especially  fits  them  for  conducting  mate- 
rials lengthwise  through  the  stem,  while  their  dovetailed 
arrangement  increases  their  surface-contact  and  so  pro- 
motes the  diffusion  of  liquid  while  at  the  same  time  it 
gives  them  great  mechanical  strength.  Let  us  now  in- 
vestigate in  the  same  manner  the  wood  of  the  Pine 
(Fig.  138).  Here  we  find  only  tracheids.  The  only 
thing  which  resembles  a  duct  is  the  resin  duct  {rd) , 
which  does  not  convey  water,  but  contains  resin,  scat- 
tered in  irregular  drops.  The  tracheids  are  large  and 
are  provided  with  very  large  bordered  pits.  Make  a 
careful  comparison  of  the  wood  of  the  Oak  and  the 
Pine. 

A  very  good  way  to  study  wood -cells  is  by  isolating 
them.  Place  some  rather  thick  longitudinal  sections  in 
a  dish,  add  a  few  crystals  of  potassium  chlorate,  and 
pour  in  enough  nitric  acid  to  cover  them.  Set  the  mix- 
ture outside  the  window  until  fumes  cease  to  come  off, 
then  wash  the  sections  in  water  and  tease  out  with 
needles,  if  necessary.  The  wood-cells  will  then  have 
separated  from  each  other  and  may  be  studied  in  their 
isolated  condition ;  in  this  way  we  may  learn  the  length 
of  the  tracheids  ;  to  ascertain  the  length  of  the  ducts 


fa£ittJ€cd    sprtnytt/ccd  iast 

^  ^     earn  unt^       ^ 


ccr-p 


«1  1^1    I    !v1IIIIJtJM   1111  III  illl  Ulvlli'    Bf&a 

v/        ^ ^  V4 ^'THm^iumhL,  at  sp  \b^{*t>np^ M 

^atl  weed  Spriny  weed      *^''^ — haSt 

LONaiTUDlNAL  ^ECT/QN 

138.  Pine  branch:  {ck)  cork,  {cc)  cork  cambium,  {col)  collenchsmia,  {cor.-p)  cor* 
tical  parenchyma,  (rd)  resin  duct,  {oh)  old  bast,  {sp)  sieve-plate,  {si)  sieve- 
tube,  {bp)  bast  parenchyma,  (p)  pit,  {mr)  medullary  ray. 


THE    WOBK  OF  STEMS 


237 


we  must  employ  another  method.  For  this  purpose  we 
force  one  end  of  the  stem  through  a  hole  in  the 
center  of  a  rubber  stopper  which  fits  into  the  air- 
pump  in  the  manner  shown  in  Fig.  139. 
If  we  now  place  the  free  end  of  the  stem 
in  water  and  withdraw  the  piston,  water 
will  be  drawn  up  into  the  ducts.  We  must 
place  in  the  fluid  some  coloring  matter 
which  cannot  pass  through  the  cell -wall; 
for  this  purpose  we  may  use  India  ink  or 
cinnabar  rubbed  up  fine  in  water  and 
filtered  through  filter  paper  so  as  to  take 
out  all  the  coarser  particles.  We  now  ex- 
haust for  about  half  an  hour,  making  as 
many  strokes  with  the  piston  as  necessary. 
If  none  of  the  coloring  matter  comes 
through,  shorten  the  stem  by  cutting  a 
piece  off  the  end  and  proceed  as  before  ; 
repeat  this  until  the  stem  is  short  enough 
to  permit  the  coloring  matter  to  pass 
through.^  If  we  now  remove  the  stem  and 
cut  it  open,  we  can  easily  ascertain  the 
length  of  the  ducts,  tracheids,  etc.,  and 
whether  there  is  open  communication  between  them. 
We  should  suppose  that  water  would  travel  faster 
in  the  open  ducts   than  in  the   closed   tracheids;    the 

iThe  liquid  may  also  be  forced  into  the  stem  by  means  of  \h.e  apparatus 
shown  in  Fig.  141. 


-k 


%. 


139.  Method  of 
injecting  a 
twig  by  means 
of  the  a  i  r  • 
pump. 


238 


EXPERIMENTS    WITH   PLANTS 


r 


Oak  would  seem  to  have  an  advantage  in  this  respect 
over  the  Pine.  In  order  to  compare  their  efficiency, 
cut  a  live  branch  of  each  about  twelve  inches  long  and 
as  free  from  leaves  or  branches  as  possible. 
Remove  the  leaves  and  branches  which 
are  present,  and  connect  the  base  of  the 
branch  by  means  of  two  or  three  feet  of 
heavy  white  rubber  tubing  to  a  glass  tube 
three  or  four  feet  long  (the  tube  may  be 
formed  of  several  pieces  joined  together 
by  rubber  tubing) .  Hold  the  tube  upright 
with  the  branch  hanging  straight  down, 
and  fill  it  with  water;  compress  the  rubber 
tube  several  times  to  expel  air.  Place  the 
branch  upright  and  secure  it  by  a  clothes- 
pin in  the  position  shown  in  Fig.  140 
(which  shows  a  slightly  different  arrange- 
ment from  the  one  here  described) .  Con- 
nect the  upper  end  with  a  piece  of  glass 
tubing  (about  six  inches  long),  in  which 
place  a  little  water.  Place  a  little  oil  on  the 
top  of  the  water  in  each  of  the  tubes.  Make 
the  joints  water-tight  by  winding  with  elas- 
(or  with  wire)  ;  close  with  sealing-wax 
any  wounds  made  by  the  removal  of  leaves,  branches, 
etc.  The  diameters  and  lengths  of  the  branches  should 
be  as  nearly  alike  as  possible.  The  height  of  the 
water-column  in   the   long  tubes   (measured  from   the 


140.  Arrange- 
ment for  f  orc- 
ing  water 
through  a 
branch. 

tic    bands 


THE    WOBK   OF   STEMS  239 

level  of  the  water  in  the  short  tube)  should  be  the 
same  in  both  cases.  Mark  carefully  the  height  of  the 
water- column  in  all  the  tubes  at  the  begnming  of  the 
experiment,  and  at  the  end  of  twenty- four  hours 
compare  the  amount  of  water  that  has  run  through 
the  two  stems,  as  indicated  by  the  rise  of  the  water- 
columns  in  the  short  tubes. 

In  order  to  gain  some  idea  of  the  energy  required  to 
force  the  water  needed  for  transpiration  through  the 
stem  in  each  of  these  trees,  we  may  first  ascertain  the 
normal  rate  of  flow  and  then  the  amount  of  energy 
required  to  force  water  through  the  branch  at  the 
same  rate.  Cut  vigorous  leafy  branches,  one  of  Oak 
and  one  of  Pine,  three  or  four  feet  long,  and  place 
them  in  Jars  of  water,  on  the  surface  of  which  we 
pour  a  little  oil  (cottonseed  or  olive)  to  prevent 
evaporation.  Having  done  this,  we  weigh  each  jar 
with  its  contents  and,  after  exposing  it  for  twenty -four 
hours  to  conditions  favorable  to  transpiration,  weigh 
again. 

We  now  take  a  section  of  a  lamp-chimney  or  of 
glass  tubing,  at  least  an  inch  in  diameter,  fit  it  at 
each  end  with  a  stopper  of  rubber  or  paraffined  cork, 
and  insert  air-tight  in  one  of  these  corks  a  glass  tube 
(one-eighth  to  one-fourth  inch  in  diameter),  about 
three  feet  long.  Now  heat  the  tuoe  and  bend  it  till  it 
comes  in  contact  with  the  large  tube  (as  shown  in  Fig. 
141),    and    secure   it  firmly   in    this  position   by  wire. 


240 


EXPERIMENTS    WITH  PLANTS 


141.  Modification 
of  arrangement 
shown  in  Fig. 
140. 


Trim  away  from  the  Pine  branch  all  its 
leaves  and  twigs  (the  wounds  made  in  so 
doing  should  be  covered  with  sealing- 
wax),  insert  the  base  of  the  branch  air- 
tight in  the  cork,  fill  the  large  tube  brimful 
of  water  and  insert  the  cork  with  its 
branch  so  as  to  exclude  air  as  much  as 
possible.  Pass  a  wire  over  both  corks,  as 
shown  in  the  figure,  and  secure  it  firmly. 
Attach  a  glass  tube  five  or  six  inches  long 
to  the  top  of  the  branch,  and  pour  mer- 
cury into  the  long  tube  until  there  is  suffi- 
cient pressure  to  make  water  flow  through 
the  branch  at  the  same  rate  as  it  flowed 
when  intact  (as  shown  by  the  weighing) . 
Perform  the  same  experiment  with  the 
Oak  branch.^ 

The  same  experiment  may  be  per- 
formed by  basing  the  comparison  on  the 
rapidity  of  rise  of  the  sap  as  shown  by  eosin 
solution  (instead  of  on  the  amount) .  In  this 
case  two  similar  branches  from  the  same 
tree  should  be  compared,  one  being  placed 
intact  in  eosin  solution,  the  other  stripped 
and  connected  with  the  tube  as  before,  so 
as  to  force  the  eosin  solution  throu2:h  it. 


1  It  is  possible  to  perform  the  experiment  on  short  twigs  by  pouring  water 
instead  of  mercury  into  the  long  tube. 


THE    WORK   OF   STEMS  241 

It  is  of  course  impossible  to  estimate  from  the  re- 
sults of  the  above  experiment  how  much  pressure  is 
required  to  force  water  to  the  top  of  a  Pine  tree  fifty 
or  one  hundred  feet  high,  but  we  know  that  it  must  be 
a  much  greater  amount  than  is  needed  to  force  it 
through  a  short  branch  such  as  we  have  used.  We  have 
at  least  found  out  that  a  powerful  force  is  at  work. 

Is  the  water  raised  by  a  force  acting  from  above 
(i.  6.,  pulled  up),  or  by  a  force  acting  from  below  (i.  e., 
pushed  up),  or  by  both  methods?  As  we  have  already 
learned,  there  is  in  the  leafy  branch  a  powerful  force 
at  work  lifting  the  water,  and  this  too  when  the  branch 
is  completely  separated  from  the  root.  In  this  case 
the  force  must  reside  in  the  stem  or  in  the  leaves. 
Determine  the  amount  and  rapidity  of  sap -flow  in  a 
leafy  branch,  as  compared  with  a  similar  branch 
deprived  of  its  leaves  (and  with  the  wounds  caused  by 
their  removal  sealed  with  sealing-wax) .  Does  the  result 
indicate  that  the  force  resides  principally  in  the  leaves? 

It  would  appear  probable  from  this  and  other  experi- 
ments Vvdiich  have  been  made  that  the  water  is  pulled 
up  by  a  force  acting  from  above.  If  this  were  the  case 
it  would  create  a  partial  vacuum  in  the  ducts  whenever 
the  supply  of  water  from  the  roots  ran  low.  Do  we 
find  any  evidence  of  such  a  state  of  things  ?  Allow  a 
vigorous  plant  (Squash,  Sunflower,  etc.)  to  wilt 
slightly,  thus  showing  that  the  supply  of  water  from 
the   root  is   running  low.     Now  bring   a  part  of  the 

P 


242  J^JXPl'Jh'IMJ^XTS    WITH   PLANTS 

steni  under  eosiii  solution  in  a  shallow  pan,  and  cut 
the  stem  underneath  the  liquid  by  a  quick,  clean  stroke 
of  a  sharp  knife  or  scissors.  After  two  or  three  min- 
utes, remove  the  stem  and  determine  how  far  the  eosin 
has  penetrated. 

In  what  manner  do  the  leaves  exert  this  force  ?  We 
have  already  learned  (page  122)  that  the  root-hairs 
draw  up  water  by  reason  of  the  water -attracting  sub- 
stances which  they  contain.  We  determined  the  water- 
attracting  power  of  the  root- hairs  by  placing  them  in 
weak  solution  of  salt  or  sugar  and  increasing  the 
strength  of  the  solution  until  it  attracted  water  from 
them  and  they  became  flabby;  we  m.ay  do  the  same 
with  the  leaves,  and  we  then  find  that  it  takes  a  much 
stronger  solution  to  attract  water  from  them  than  from 
the  root -hairs.  If,  then,  the  leaves  are  so  much  richer 
in  water-attracting  substances  ^  than  the  root -hairs,  the 
most  probable  explanation  seems  to  be  that  they 
attract  water  from  the  root -hairs  through  the  interven- 
ing cells  and  ducts,  and  so  supply  what  they  lose  by 
evaporation.  It  is  at  present  doubtful  whether  this 
explanation  can  account  for  the  rise  of  sap  for  more 
than  150  to  200  feet.^ 

1  The  youngest  leaves,  which  are  richer  in  water-attracting  substances  than 
the  old  ones,  are  also  the  first  to  be  colored  when  a  short  piece  of  stem  is 
placed  in  eosin;  this  indicates  that  they  attract  water  more  powerfully  than 
the  older  leaves. 

2  Two  factors  which  are  little  understood  as  yet  must  be  reckoned  with; 
the  tensile  strength  of  the  water-column  and  the  frictional  resistance  of  the 
ducts,  tracheids,  etc. 


THJiJ    WOBK   OF  STUMS 


243 


The  fact  that  the  run  of  sap  commences  in  the 
spring  before  the  leaves  appear  (as  in  the  Sugar 
Maple,  etc.)  is  apparently  due  to  the  formation  at 
that  time  of  large  quantities  of  sugar  and  other  water- 
attracting  substances  in  the  stem  which  draw  up  the 
water  in  large  quantities. 

It  is  a  matter  of  common  observation  that 
at    certain   times   of   the   year   many  plants 
bleed    (i.    e.,    exude    water)    when    cut    or 
trimmed.    Test  some  vigorous,  well- watered 
plants   in   regard    to    this    point    (especially 
Squash,   Sunflower,  Dahlia,  Begonia,   Corn, 
etc.)  by  cutting  off  the  plant  near  the  ground 
and  connecting  the  stump  to  a  glass  tube  by 
means  of  a    section  of  rubber  tubing  (see 
Fig.  142).    Pour  a  little  water  in  the 
tube  and   support   it   in   an  upright 
position.    Place   a   little   oil    on   the 
water  and  mark  the  height  at  which 
it    stands.     In    favorable    cases    the 
water  will  rise  in  the  tube;    this  is 
due  to  what  is  known  as  root- pres- 
sure; some   observed  cases  of  root- 
pressure  show  that  it  could,  in  cer- 
tain plants,  under  favorable  circum- 
stances, raise  the  water  manv  feet; 

'  142.  Method  of  measuring 

but     at     the    time    of     yeai*     when  ^^^  amount  of  bieea- 

"  iug    from    a     stump 

transpiration  is  greatest  little  or  no  (root  pressure). 


244  EXPERIMENTS    WITH  PLANTS 

root-pressure  is,  as  a  rule,  observable.  We  may  there- 
fore leave  it  out  of  account  in  this  connection. 

The  amount  of  water  necessary  to  supply  the  leafy 
crown  of  a  lar^e  tree  must  be  very  large,  and  we 
might  naturally  suppose  that  all  the  wood  of  the  trunk 
is  employed  in  conveying  it.  It  is  often  noticed,  how- 
ever, that  in  old  trees  the  heart- wood  decays  and 
leaves  the  trunk  hollow  without  affecting  the  health  of 
the  tree.  Moreover,  on  sawing  off  a  tree  or  branch  six 
or  eight  inches  in  diameter  and  placing  the  cut  end 
in  eosin  solution,  we  find  that  the  colored  liquid  does 
not  rise  in  the  inner  portion  of  the  wood  but  only  in 
the  outer.  (In  case  this  experiment  is  carried  out,  the 
tree  may  be  removed  from  the  solution  and  allowed 
to  dry  with  its  leaves  on  and  will  serve  for  years  as 
demonstration  material.)  The  cells  of  the  interior 
portion  of  the  wood  are  more  or  less  stopped  up  with 
various  substances,  and  appear  more  deeply  colored 
than  those  of  the  outer  portion;  this  inner  portion  is 
called  the  heart-wood^  and  the  outer  the  sap-wood. 

If  water  is  prevented  from  traveling  in  the  sap-wood, 
can  it  travel  in  the  heart- wood  instead  ?  We  may 
answer  this  question  by  cutting  a  ring-shaped  groove 
all  around  the  tree  or  branch  deep  enough  to  go 
through  the  sap-wood  and  prevent  the  water  from 
traveling  in  it.  The  wilting  of  the  leaves  will  indicate 
the  extent  to  which  the  water  current  is  interfered 
with.    No  one  who  has  seen  this  experiment  carried 


THt:    WORK   OF    STEMS  245 

out  can  thoughtlessly  destroy  a  tree  by  hacking  it 
without  realizing  the  injury  he  is  inflicting. 

In  connection  with  the  study  of  wood  and  its  struc- 
ture, take  up  as  far  as  possible  the  practical  aspects  of 
the  matter.  What  is  meant  by  the  seasoning  of  wood? 
What  does  this  involve!  How  is  it  best  accomplished? 
Why?  Does  the  water  escape  principally  through  the 
sides  or  through  the  end  of  the  log?  What  occurs  if 
the  end  is  painted  or  rendered  water-proof?  Does  the 
wood  crack  less  if  allowed  to  season  with  the  leaves 
on?  What  kinds  of  wood  shrink  most  in  drying? 
What  kinds  contain  most  water?  ^ 

What  determines  the  usefulness  of  a  wood?  What 
kinds  of  woods  are  used  for  the  various  parts  of 
wagons?  Why?  Can  you  explain  their  peculiarities  by 
a  study  of  their  cell  structure?  What  woods  growing 
in  your  region  are  useful  in  any  way?  Why?  What 
woods  last  longest  when  exposed  to  the  weather? 
What  is  the  best  treatment  to  preserve  woods ?2 

Learn  how  to  read  the  history  of  a  branch  by  the 
inspection  of  the  scars  on  it.^  In  some  cases  (e.g., 
Alder)  this  history  can  be  read  back  many  years. 

As  the  sap-wood  grows  older  it  changes  into  heart- 

1  In  regard  to  the  absorption  of  water  by  wood,  see  pag:e  68. 

2  See  articles  in  the  Year-Book  of  the  U.  S.  Department  of  Agriculture  for 
1894  by  Fernow;  for  1896  by  Roth;  for  1903  by  von  Schrenk.  On  the  manage- 
ment of  forests,  etc.,  see  Roth:  "First  Book  of  Forestry";  Pinchot:  "Primer  of 
Forestry";  also  articles  in  the  Year-Book  for  1895  by  Fernow;  for  1898  and  1899 
by  Pinchot. 

3 See  Bailey:  "Lessons  with  Plants,"  p.  73  ff. 


246  EXPJ<JliIMENTS    MITE    PLANTS 

wood,  and  new  sap-wood  muist  be  formed  to  take  its 
place.  If  we  examine  sections  of  the  Oak  (Fig.  135) 
or  Pine  (Fig.  138),  we  can  see  how  the  new  wood  is 
formed.  At  the  outer  edge  of  the  wood  is  a  tissue 
called  the  cambium,  composed  of  very  small,  rapidly 
growing  cells.  We  can  see  how  these  cells  grow  larger 
to  form  wood  on  one  side  and  bast  on  the  other  (this 
is  well  shown  in  the  Squash,  Fig.  133) .  In  the  middle 
of  the  cambium  layer  the  cells  divide  frequently  into 
two,  thus  forming  more  cells,  which  ultimately 
develop  into  wood  or  bast.  If  we  make  sections  of  the 
extreme  tip  of  the  stem,  where  the  bundles  are  still 
separate,  we  find  that  the  cambium  layer  grows  out 
from  the  bundles  and  unites  to  form  a  ring,  which 
soon  forms  wood  and  soft  bast  in  a  complete  circle 
around  the  stem. 

When  we  separate  the  bark  of  a  tree  from  the  wood, 
we  find  between  the  two  a  white,  glistening,  juicy 
layer;  this  is  the  cambium.  If  we  carefully  make  an 
incision  in  the  bark  of  a  tree  (preferably  a  young  tree 
on  which  the  bark  is  thin),  and  slip  a  thin  piece  of 
metal  (a  ten- cent  piece  hammered  thin  is  very  good 
for  this  purpose)  between  the  cambium  and  the  wood, 
it  will  be  found  in  the  course  of  a  year  to  be  covered 
with  a  thin  veneer  of  wood  as  the  result  of  the  activity 
of  the  cambium.  You  may  easily  try  this  experiment 
for  yourselves.  Axe -heads,  iron  bolts,  etc.,  have  been 
taken  from  the  heart  of  trees  which  were  covered  by 


THE    WORK   OF   STEMS  247 

many  annual  rings  of  wood.  The  annual  ring  of  wood 
is  the  growth  made  by  the  cambium  in  one  year.  The 
wood  formed  in  autumn  (or  toward  the  end  of  the 
season  of  growth)  is  much  denser  and  harder  than  that 
formed  in  the  spring  and  composed  of  smaller  cells 
(Figs.  135  and  138) ;  the  difference  is  apparent  to  the 
naked  eye  and  the  rings  may  be  easily  counted,  thus 
fixing  the  age  of  the  tree  (see  Fig.  145) .  If,  on  account 
of  drought,  destruction  of  the  leaves  by  insects,  or  for 
any  other  reason,  there  are  two  seasons  of  growth  in 
a  year,  there  are  two  more  or.  less  sharply  defined 
rings.  The  formation  of  denser  wood  in  the  fall  is 
probably  due  partly  to  the  unfavorable  conditions  of 
growth  then  prevailing  and  partly  to  the  "binding"  of 
the  bark,  which  gets  tighter  as  the  expanding  wood 
stretches  it,  so  hindering  the  growth  and  making  the 
cells  smaller.  Cut  a  section  (about  one -fourth  of  an 
inch  thick)  from  a  twig  during  the  growing  season. 
Slit  the  bark  on  one  side  and  peel  it  off  carefully. 
Now  replace  the  ring  of  bark  on  the  twig;  can  you 
make  the  ends  meet  ?  What  does  this  show  in  i-egard 
to  the  stretched  condition  of  the  bark!  Fruit-growers 
often  slit  the  bark  of  trees  in  the  spring  with  the  point 
of  a  knife,  in  order  to  allow  the  wood  to  expand: 
washes  of  soap  or  lye  are  also  used  to  soften  the  bark. 
Trees  exposed  to  a  prevailing  wind  grow  thicker  in  the 
direction  in  which  the  wind  blows;  this  is  believed  to 
be  due  to  the  stretching  and  loosening  of  the  bark  on 


248 


JDXPERIMENTS    WITH   PLANTS 


opposite  sides  by  the  bending  of  the  tree  in  the  wind. 
Wherever  the  outer  surface  of  the  wood  is  concave, 
each  new  layer  of  wood  finds  less  room  to  spread  out, 
and  hence  is  obliged  to  thicken  up  more  and  more 
until  a  huge  buttress  may  be  formed  beneath  a  branch, 
as  is  shown  in  Fig.  142a.    All  concavities  thus  tend 

to  fill  up  in  time. 
Experiments 
may  be  made  to 
test  the  effect  of 
^'binding"  on  the 
growth  of  the 
wood  by  wrap- 
ping a  branch 
securely  with 
wire    during   the 


142a. 


Buttress  formed  on  the  lower  side  of  a  branch 
where  it  joins  the  trunk. 


growmg  season 
and  investigating  it  at  the  close  of  the  season.  Try 
also  the  experiment  of  slitting  the  bark  with  a  knife. 

The  growth  of  the  cambium  adds  each  year  a  layer 
to  the  bark,  as  well  as  to  the  wood,  so  that  although 
the  bark  continually  wears  off  on  the  outside  it  grows 
thicker  each  year  as  the  tree  grows  older.  (The  stems 
of  Monocotyledons  have  no  cambium  and  do  not  grow 
thicker  from  year  to  year.) 

It  is  by  means  of  the  growth  of  the  cambium  that 
the  scion  and  stock  unite  in  grafting.  Find  out  what 
you  can  about  this.    Make  sections  through  the  place 


THE    WORK   OF   STEMS 


249 


of  union  and  examine  under  the  microscope.  If  possi- 
ble, try  some  experiments  in  grafting.  For  directions 
see  Hunn  and  Bailey:  "The  Practical  Garden 
Book";  also  consult  some  one  who  is  skilled  in  the 
matter. 

The  cambium  is  not  the  only 
portion  of  the  stem  that  grows,  for, 
as  we  have  already  learned,  the 
stem  grows  in  length  at  the  tip.  We 
may  divide  the  tip  into  three  re- 
gions (Fig.  143) :  {a)  the  extreme 
end,  occupied  by  a  bud  in  which 
leaves  are  continually  being  formed ; 
we  may  call  this  the  formative  re- 
gion; (h)  the  elongating  region^  just 
back  of  the  formative  region  (see 
page  77),  and  (c)  the  maturing  re- 
gion (region  of  differentiation),  in 
which  the  various  tissues,  having 
ceased  almost  entirely  to  grow  in  size^  assume  their 
characteristic  forms  and  structures.  It  will  be  noticed 
that  the  buds  are  formed  in  the  axils  of  leaves  (i.  e., 
just  above  the  junction  of  the  leaf  and  stem) ;  excep- 
tions to  this  are  the  buds  formed  from  callus  (see 
page  263)  and  the  buds  formed  on  roots,  e.  g.,  the 
buds  which  grow  up  into  sprouts  or  suckers  from  the 
roots  of  fruit  trees.  Poplars,  Elms,  etc. 

A  peculiar  method  of  growth  at  the  joints  or  nodes 


143.  Terminal  part  of  a 
growing  branch:  (a) 
formative  region,  (&) 
elongating  region,  (c) 
maturing  resion(rcgion 
of  dififereutiation). 


250 


EXPERIMENTS    WITH  PLANTS 


is  found  in  the  Wandering  Jew,  Grasses  and  some 
other  plants.  Examine  some  growing  Grass  or  Grain: 
notice  how  tender  and  succulent  the  joints  are;  also 
how  much  sugar  they  contain,  as  shown  by  the  taste. 
Cut  off  a  stem  half  an  inch  above  a  joint.  Three  or 
four  inches  below  the  joint  make  another  cut  and  place 
the  piece  in  a  moist  atmosphere  with  the  base  in  water 
or  wet  sand.  The  growth  at  the  joint  will  soon  mani- 
fest itself  by  contrast  with  the  sheathing  base  of  the 
leaf  which  surrounds  it   and  which  grows  very   little 

or  not  at  all. 

In  order  to  get  a 
clear  idea  of  what 
goes  on  in  the  forma- 
tive region,  let  us 
study  a  large  bud, 
such  as  a  head  of 
Cabbage  or  Brussels 
Sprouts  (Fig.  .144). 
The  end  of  the  stem 
is  seen  to  be  conical; 
at  its  extreme  tip  are 
small  outgrowths  (eas- 
ily seen  with  a  hand- 
lens) ;  these  are  the 
youngest  leaves. 
Next     to     these    are 

144.     Bud  of  Brussels  Sprouts  cut  kMi«thvvise:  {f)    '        t     i    ,  i  it 

fibrous  bundles,  {bi)  the  crumpled  leaf-blade.  Sllgntly       OlCier       OUOS, 


Tn±]    WOEK    OF    STFMS  251 

beginning  to  show  a  differentiation  into  blade  and 
stalk.  A  little  lower  down  the  thin  blade  {hi)  of 
the  leaf  is  seen,  crumpled  in  a  wavy  manner  between 
the  successive  thickened  veins.  In  the  axil  of  each 
leaf  is  a  tiny  bud,  a  miniature  of  the  larger  one  in 
which  they  are  contained.  Notice  that  the  fibrous 
bundles  (/",/)  extend  almost  to  the  tip  of  the  stem  and 
send  off  branches  to  each  leaf  and  each  bud.  You  can 
trace  their  course  clearly  by  placing  the  cut  end  for  a 
a  time  in  eosin  solution. 

Notice  how  the  overlapping  of  the  older  leaves  pro- 
tects the  younger  ones.  Protection  from  drying  is  very 
necessary,  for  the  younger  leaves  are  exceedingly  sen- 
sitive. Remove  most  of  the  outer  leaves  and  note  the 
effect  on  those  which  remain. 

Remove  the  bud -scales  from  winter -buds,  and 
note  the  effect.  The  water -proof  varnishes  of  such 
bud  -  scales  are  an  excellent  protection  against  drying 
(the  popular  notion  that  bud -scales  protect  against 
cold  is  a  fallacy) ;   see  also  pages  213  and  214. 

The  protection  of  the  tip  of  the  stem  by  the  over- 
lapping bud- scales  and  young  leaves  is  due  to  the  fact 
that  these  organs  grow  faster  on  the  lower  side  than 
on  the  upper,  thus  causing  them  to  curve  inward. 
When  the  bud  opens,  the  reverse  process  occurs, 
growth  becoming  more  rapid  on  the  upper  side.  In 
some  leaves  this  condition  persists,  giving  them  a  per- 
manently curved  appearance  or  causing  them  to  flatten 


252  EXPERIMENTS    WITH   PLANTS 

themselves  out  on  the  ground  as  in  the  Dandelion 
(experiment  by  placing  a  Dandelion  upside  down  with 
its  root  wrapped  in  moist  cotton) .  Study  the  unrolling 
of  Fern  leaves. 

In  this  connection  let  us  consider  the  general  con- 
ditions of  growth.  Every  one  is  familiar  with  the  ex- 
pression "  growing  weather,"  which  clearly  indicates 
that  growth  depends  on  certain  conditions.  We  may 
experiment  on  three  of  these  —  namely,  warmth,  mois- 
ture and  light.  For  this  purpose  obtain  a  lot  of  seed- 
ling plants  (of  the  same  kind)  as  similar  as  possible 
in  respect  to  vigor  and  general  condition.  They  must 
be  grown  in  pots  or  boxes. 

{a)  Temperature. —  Select  three  pots,  and  mark  the 
stem  of  each  plant  with  ink  two  inches  from  the  tip. 
Cover  each  pot  with  an  opaque  cover  (a  pasteboard 
cylinder  or  box  will  answer),  to  exclude  the  light. 
Insert  a  thermometer,  if  possible,  in  each,  so  that  it 
may  be  conveniently  observed.  Place  one  pot  in  the 
warmest  spot  about  the  building,  another  in  the 
coolest,  and  the  remaining  one  in  a  place  of  medium 
temperature.  After  three  or  four  days,  measure  tlie 
growth  of  each. 

(&)  Moisture.  —  Use  two  potted  plants,  provided 
with  opaque  covers  to  exclude  light,  keeping  them 
all  together  in  a  spot  where  the  temperature  is  most 
favorable  to  growth.  Before  commencing  the  experi- 
ment, allow  one  of  them  to  suffer  from  lack  of  water, 


THE    WOBK  OF   STEMS  253 

keeping  the  other  well  watered.  Then  place  the  covers 
on  them  and  observe  the  growth  as  before. 

(c)  Light. —  Repeat  the  experiment,  giving  both 
pots  of  plants  plenty  of  water  and  warmth  (the  same 
amount  to  each),  but  keeping  one  covered  with  an 
opaque  cover  while  the  other  is  exposed  to  strong 
light.  Do  plants  grow  faster  during  the  day  or  during 
the  night? 

The  growth  of  the  stem  requires  a  great  deal  of 
food.  Test  the  growing  portion  (especially  the  forma- 
tive region)  for  food  substances  (for  fat,  use  the 
alcanna  test,  page  259).  Study  especially  the  behav- 
ior of  starch  in  buds  (e.  g.,  buds  of  Hawthorn, 
Maple,  Linden,  Lilac,  etc.).  In  general  the  embryo 
leaves  contain  no  starch  in  the  fall,  although  there  is 
plenty  in  the  tissue  just  beneath  them.  In  the  spring 
it  wanders  into  the  young  leaves  and  furnishes  material 
for  their  growth.  Buds  furnish  nutritious  food  to 
many  kinds  of  animals.  How  are  the  food  substances 
brought  here  from  the  leaves  !  See  if  you  can  trace 
their  paths  through  the  stem.  This  will  probably  be 
easier  in  the  case  of  starch  than  in  the  case  of  the 
other  substances.  Starch  cannot  pass  through  the 
walls  of  the  cells  which  compose  the  plant,  but  it  is 
readily  changed  into  sugar,  which  can  pass  from  cell 
to  cell  and  so  reach  the  growing  region;  when  it 
arrives  there  it  may  be  changed  into  fats,  oils,  or  even 
into  proteid  (by  combining  with  nitrogen,  sulphur  and 


254  EXPEFTMFjyTS    WITH   PLANTS 

phosphorus) ;  it  is  probable  that  in  this  process  oxalic 
acid  is  formed,  which  unites  with  lime  to  form  the 
numerous  crystals  of  oxalate  of  lime  which  are  seen  in 
the  neighborhood  of  the  bud:  they  are  easily  observed 
with  the  low  power  of  the  microscope  (see  also  Fig. 
135,  cr).  The  sugar  may  be  changed  temporarily  into 
starch,  not  only  in  the  growing  region  but  in  the  cells 
through  which  it  travels  to  get  there;  and  for  this 
reason  it  is  easy,  in  most  cases,  to  trace  its  path  by 
the  application  of  iodine  solution  to  the  cut  surfaces 
of  a  stem  divided  lengthwise. 

To  trace  the  proteid  substances  may  not  be  so  easy 
unless  we  have  a  favorable  plant,  like  the  Squash  or 
the  Pumpkin.  On  cutting  across  the  stem  of  a  Pump- 
kin, the  proteid  substances  at  once  ooze  out  at  certain 
spots  and  coagulate.  The  stem  may  be  laid  for  a  time 
in  alcohol  (to  coagulate  the  proteid  and  extract  the 
chlorophyll),  and  the  nitric  acid  test  (also  the  sul- 
phuric acid  and  sugar  test  described  on  page  166)  may 
then  be  applied.  In  less  favorable  cases  iodine  may  be 
applied;  this  turns  proteids  brown  (not  blue  or  black). 
(It  may  be  necessary  to  use  a  hand -lens  or  a  com- 
pound microscope.)  Our  examination  of  the  Squash 
stem  shows  us  that  the  proteids  are  contained  princi- 
pally in  the  bast.  The  bast  lies  on  both  sides  of  the 
wood  and  is  composed,  like  the  wood,  of  large  and 
small  cells.  The  large,  wide  cells,  called  sieve-tubes 
{st^  Fig.  loel),  are,  as  we  see  in  sections,  really  long 


Tilt:    WOliK   OF   STUMS  255 

tubes  with  openings  in  their  end- walls  through  which 
the  proteids  may  pass ;  the  importance  of  these  open- 
ings lies  in  the  fact  that  most  proteids  cannot  pass 
through  the  cell -wall  and  hence  could  not  be  trans- 
ported to  the  growing  regions  were  it  not  for  the  sieve- 
tubes.  What  causes  the  proteids  to  move  in  the 
sieve -tubes  is  not  definitely  known,  but  the  pressure 
on  the  surrounding  cells  on  the  sieve -tubes,  which 
causes  the  proteids  to  flow  out  when  the  stem  is  cut, 
must  help  to  force  proteids  into  the  young  and  grow- 
ing portions  of  the  plant,  and  the  bending  of  the  plant 
in  the  wind  probably  assists  this. 

The  smaller  cells  of  the  bast  are  of  two  kinds, 
those  which  are  closely  connected  with  the  sieve -tubes 
and  whose  end -walls  correspond  with  theirs,  hence 
called  the  companion -cells  (cr),  and  shorter  cells, 
called  the  bast  parenchyma  (hp) .  The  function  ot 
these  two  kinds  of  cells  is  not  known,  but  it  is 
conjectured  that  they  assist  in  some  way  in  the 
transportation  of  tlie  proteids. 

The  openings  in  the  end -walls  of  the  sieve- tubes 
may  be  easily  studied  in  the  cross- section  {sp,  Fig. 
133),  where  they  are  seen  to  be  so  numerous  as  to 
give  the  wall  a  sieve-like  appearance,  hence  the  name 
sieve -plate  is  applied  to  these  walls.  The  bast  may  be 
traced,  in  connection  with  the  wood,  clear  up  into  the 
leaf  and  also  down  into  the  root  (see  Fig.  90).  Most 
plants  are  not   so  well   provided  with  sieve -tubes  as 


256  EXPERIMENTS    WITH   PLANTS 

the  Squash  or  Pumpkm.  The  usual  arrangement  is 
a  single  mass  of  bast  lying  outside  the  wood,  instead 
of  both  outside   and  inside,   as   in  the  Squash. 

If  we  examine  a  branch  of  a  tree  (see  Figs. 
135  and  138)  we  find  the  bast  lying  just  outside  the 
cambium.  In  the  stems  illustrated  the  sieve -plates 
occur  on  the  side -walls  as  well  as  on  the  end -walls; 
this  is  quite  common  in  trees;  it  permits  a  more  rapid 
transfer  of  proteids  from  cell  to  cell.  The  outer  part 
of  the  bast  soon  dies  and  then  becomes  crushed  by  the 
pressure  of  the  surrounding  cells:  this  is  shown  in 
Fig.  138  {oh) .  As  the  branch  grows  older,  thin  layers 
of  cork  are  formed  here  and  there  in  the  rind,  cutting 
off  small  portions  of  it  from  the  interior;  these  por- 
tions die  and  eventually  fall  away;  the  cork -formation 
finally  encroaches  on  the  bast.  The  result  is  harh^ 
which  has  an  inner  portion  consisting  of  living  cells 
and  an  outer  portion  consisting  of  cells  which  have 
become  dry  and  dead;  these  cells,  even  though  dead, 
render  valuable  service  to  the  plant,  since  they  pro- 
tect it  against  insects,  fungi,  gnawing  animals,  fire 
and  many  other  foes.  Notice  how  quickly  the  cam- 
bium and  other  tissues  dry  up  and  die  whenever  the 
bark  is  removed.  (Protection  of  the  stem  against  ani- 
mals is,  in  many  cases,  afforded  by  hairs  and  spines; 
see  page  221.) 

What  happens  if  we  ring  the  tree  so  as  to  prevent  the 
proteids  from  passing  downward  in  the  soft  bast?    To 


THE    WORK   OF    STEMS  257 

answer  this  question  we  take  a  cutting,  preferably  of 
Willow,  about  five  inches  long  (cut  so  that  the  lower 
cut  surface  comes  just  below  a  bud)  and  ring  it  just 
above  the  lowest  bud  by  removing  a  ring  of  bark 
about  a  quarter  of  an  inch  wide,  so  as  to  lay  bare 
the  wood. 

We  now  place  the  cuttings  in  a  jar  of  water  so  that 
they  stand  upright,  about  half  submerged  (the  ring 
or  girdle  should  be  under  water) .  Under  these  con- 
ditions they  put  forth  roots  and  shoots,  whose  relative 
development  above  and  below  the  ring  will  indicate  the 
relative  supply  of  nourishment.  The  experiment  must 
be  continued  for  some  weeks. 

Inasmuch  as  in  ringing  we  cut  away  the  rind  or 
cortex  in  which  the  starch  and  sugar  chiefly  travels, 
we  may  institute  a  control  experiment  to  see  how  far 
this  affects  the  result  by  ringing  some  cuttings  in  such 
a  way  as  to  cut  the  rind  only  but  not  the  soft  bast. 
At  the  end  of  the  experiment,  test  for  starch.  Does  it 
accumulate  in  the  cortex  above  the  cut? 

Ringing  is  often  practiced  in  grape  culture.  The 
branch  is  ringed  some  distance  below  the  young  cluster 
of  grapes,  and  the  food  which  would  otlierwise  pass  down 
through  the  cortex  and  soft  bast  is  i-etained  and  used 
by  the  growing  fruit,  which  grows  to  an  unusual  size. 

In  testing  trees  for  food  substances,  we  find  con- 
siderable starch  in  the  wood,  and  on  tracing  it  back 
find    that  it   travels    thither   in    the    so-called    silver 


258  EXPEinMKXT^  wrrn  plais'ts 

^raiii  of  the  wood,  Avhieli  runs  from  the  center  out- 
ward to  the  bark  at  right  angles  to  the  ordinary  grain. 
On  splitting  an  Oak  stem  squarely  in  two,  this  silver 
grain  is  very  conspicuous  and,  on  testing,  is  found 
to  be  filled  with  starch.  In  sections  (Figs.  135  and 
138,  mr)  the  silver  grain  is  seen  to  consist  of  long, 
tubular  cells  like  the  wood- cells  (ducts  are  absent) 
running  in  a  radial  direction,  at  right  angles  to  the 
course  of  the  wood -cells.  The  silver  grain  is  called 
by  botanists  the  medullary  rays  (medulla  means  pith) ; 
they  serve  as  channels  of  communication  between  the 
wood- cells  and  the  cells  of  the  outer  portion  of  the 
stem;    they  may  convey  food,  water  or  gases. 

Why  is  so  much  starch  conveyed  to  the  wood  ?  Little 
or  no  growth  is  taking  place  in  that  portion  of  the 
wood  to  which  most  of  the  starch  is  conveyed ; 
moreover,  the  amount  of  starch  increases  instead  of 
diminishes  during  the  growing  season.  Just  after  the 
leaves  have  fallen  off  the  wood  is  very  rich  in  starch, 
while  the  fallen  leaves  contain  practically  no  food 
substances  of  any  sort  (test  this  matter).  It  would 
appear  that  the  starch  is  conveyed  from  the  leaves  to 
the  wood  for  the  purpose  of  storing  it  up  there.  Not 
only  in  the  wood  but  also  in  rind  or  cortex  do  we  find 
starch  stored  up  at  this  time  of  year.  Later  on,  during 
the  winter,  we  find  that  some  of  the  starch  has 
disappeared,  but  on  testing  we  find  an  increase  in  the 
amount  of  sugar;  we  conclude,  therefore,  that  a  part 


THE    WORK   OF   STEMS  259 

of  the  starch  has  been  converted  into  sugar;  in  the 
spring,  with  the  approach  of  warmer  weather,  the 
starch  reappears  and  remains  until  it  is  used  up  by 
the  growth  of  the  new  leaves  and  branches.  On 
account  of  the  starch  which  they  contain  in  winter, 
such  trees  as  the  Oak,  Willow,  Hazel,  Lilac,  etc.,  are 
called  starch  trees.  On  the  other  hand,  many  trees, 
such  as  the  Linden,  Birch,  etc.,  contain  no  starch  in 
midwinter;  it  has  been  transformed  into  fat,  as  is 
indicated  on  placing  sections  in  alcanna  tincture. ^ 
Such  trees  are  called  fat  trees  ;  on  the  approach  of 
warmer  w^eather  in  spring  the  fat  is  changed  back  into 
starch.  Does  the  temperature  seem  to  control  these 
changes?  Bring  in  a  branch  of  Linden  in  midwinter 
and  test  for  starch  ;  set  it  in  a  jar  of  w-ater  in  a  warm 
room,  and  after  three  or  four  weeks  test  again. 

When  the  buds  are  preparing  to  unfold  in  the 
spring,  the  sap  begins  to  run.  We  can  observe  this 
especially  well  in  the  Sugar  Maple,  Birch,  etc.,  and 
here  the  taste  of  the  sap  shows  that  it  contains  a 
considerable  quantity  of  sugar.  In  this  case,  then, 
the  sugar  travels  upw^ard  in  the  w^ood  ;  this  sugar,  as 
we  can  easily  convince  ourselves,  comes  from  the 
transformation  of  the  starch  and  serves  to  supply  the 
young  leaves  and  branches  with  material  for  their 
vigorous  spring  growth.    Investigate  other  trees,  test- 

1  This  is  obtainable  at  dm^-stores.  It  is  made  by  placinjir  alcanna  root  in 
alcohol  \intil  the  coloring  matter  is  extracted.  It  has  the  property  of  staining 
fats  and  oils  red. 


260  EXPERIMENTS    WITH    PLANTS 

ing  with  Fehling's  solution  (see  page  164)  if  neces- 
sary, and  determine  their  behavior  in  this  respect. 

The  storage  of  food  is  extremely  advantageous  for 
the  plant,  not  only  for  the  period  of  rapid  growth  in 
the  spring  but  also  for  the  period  of  flower  and  fruit. 
We  find  various  parts  of  the  plant  used  as  storage 
reservoirs,  according  to  the  particular  needs  of  the 
case.  We  may  say  that  the  problem  of  storage  has 
been  solved  by  the  plant  in  a  great  variety  of  ways. 
Storage  in  leaves  is  seen  in  seed-leaves,  in  the  scales 
of  bulbs,  and  in  the  leaves  of  succulents  (Live -for- 
ever, Century  Plant,  etc.).  Storage  in- stems  is  seen 
in  trees,  in  Cacti,  in  tubers  of  the  Potato  (examine 
the  Potato  and  notice  the  buds,  or  "eyes,"  placed  in 
regular  fashion  and  the  minute  bundles  which  are 
more  easily  seen  if  the  tuber  is  allowed  to  stand  with 
the  cut  surface  in  eosin  until  the  fluid  rises  in  the 
bundles;  these  are  indications  of  its  stem  nature), 
the  conn  of  Crocus,  the  root -stock  of  Iris,  etc. 
Storage  in  the  root  is  seen  in  the  Carrot,  Turnip,  etc. 

In  all  of  the  storage  organs  the  form  is  such  as  to 
give  a  great  bulk  with  little  exposed  surface,  and  in 
very  many  cases  they  are  sheltered  under  ground, 
where  they  are  protected  from  foes  and  transpiration 
is  lessened.  When  above  ground  they  are  usually 
protected  from  foes  by  thorns,  spines,  hairs,  etc.,  or 
by  a  bitter  or  disagreeable  taste ;  to  prevent  transpira- 
tion  they   have    much    the    same    devices    as    leaves: 


THE    WOBK   OF    STEMS  261 

bulbs,  corms,  etc.,  are  usually  protected  by  the  dead 
leaves  of  the  previous  season  which  enwrap  them. 

The  beautiful  arrangements  of  leaves  whereby  they 
spread  out  over  a  great  area  so  as  to  absorb  sunshine 
without  mutual  interference  would  not  be  possible 
without  a  proper  grouping  of  the  branches  on  which 
they  are  borne.  How  do  the  stems  aid  the  leaves  in 
securing  the  best  arrangement  ?  What  do  you  think  is 
the  most  advantageous  arrangement  of  the  branches 
(and  of  the  leaves  upon  them),  in  order  that  the 
greatest  amount  of  sunshine  may  be  absorbed  with  the 
greatest  economy  of  material?  Take  into  considera- 
tion the  daily  motion  of  the  sun.  Notice  the  difference 
between  a  tree  growing  in  the  woods  and  one  growling 
in  the  open,  where  it  receives  light  from  all  sides.  As 
soon  as  we  begin  to  study  the  forest- grown  tree  we 
notice  that  the  lower  part  of  the  trunk  appears  free 
from  limbs,  not  because  none  have  appeared  in  that 
region  but  simply  because  they  have  perished  from 
lack  of  light.  This  process  is  called  self- pruning,  and 
to  it  is  due  the  value  of  the  tree  for  lumber,  since  it 
results  in  straight  timber  free  from  knots.  In  the  tree 
grown  in  the  open  self- pruning  also  occurs,  though  to 
a  much  smaller  extent. 

There  is  a  continual  struggle  going  on  among  the 
branches  for  light  and  space,  which  results  in  stunting 
and  dwarfing  the  weaker  ones  or  in  killing  them  alto- 
gether.   Many  factors  afEect  the  result;    the  position 


262 


EXPEBIMKNTS    WITH   PLANTS 


of  the  branch,  the  supply  of  sap,  of  sunshine,  of 
elaborated  food  from  the  stem,  and  from  the  leaf  in 
whose  axil  the  branch  starts,  etc.  On  pulling  off  the 
bark  of  a  tree  (e.  g.,  of  a  Pine  or  of  an  Oak)  we  find 
under  the  bark,  projecting  from  the  wood,  numerous 
little  incipient  branches  which  have  never  been  al- 
lowed to  develop  (Fig.  145). 
By  splitting  open  the  stem, 
we  may  trace  them  inward 
toward  the  heart  through 
several  annular  rings,  thus 
determining  their  age.  Their 
growth  keeps  pace  with  that 
of  the  stem,  but  they  thicken 
scarcely  at  all ;  in  some  cases 
they  branch,  causing  the  ap- 
pearance familiar  to  us  in 
"bird's-eye  maple."  In  almost  any  good-sized  tree  we 
may  find  such  latent  buds,  as  they  are  called,  which 
for  several  years  have  patiently  awaited  their  chance 
to  develop.  If  now  the  tree  be  cut  down,  thus  remov- 
ing the  fierce  competition  of  the  upper  branches,  they 
spring  up  at  once  into  wonderfully  vigorous  growth. 
In  this  connection  study  cuttings  and  make  such 
experiments  as  are  practicable.  Do  cuttings  require  a 
light  sandy  soil  in  which  air  circulates  freely?  It  has 
been  found  that  cutting  a  plant  produces  local  fever 
just  as   in   an   animal   and    an  increased    quantity  of 


14').     Portion  of  trunk  near  ca  burl,  show 
ing  latent  buds  beneath  the  bark. 


THE    WOBK   OF   STEMS  263 

oxygen  is  consumed.  The  growth  of  the  calhis  and  of 
the  new  roots  also  reqmres  a  considerable  amount 
of  air. 

If  there  are  leaves  on  the  cutting  they  should  be 
removed  partially  or  entirely,  to  diminish  the  loss  of 
w^ater,  since  there  are  no  roots  to  keep  up  the  supply. 
Shading  the  cuttings  and  keeping  the  air  moist  assist 
greatly  in  this  respect.^ 

In  many  cases  we  find  new  branches  springing 
directly  from  the  cut  surface  of  a  limb  or  a  stump.  If 
we  examine  closely  we  find  that  these  come,  not  from 
latent  buds,  but  from  buds  newly  formed,  as  it  were 
for  the  emergency,  by  a  tissue  which  grows  out  from 
the  cambium.  This  tissue,  called  the  callus,  wdll  in 
time,  if  left  undisturbed,  cover  over  the  cut  surface 
entirely.  This  is  of  the  utmost  advantage  to  the  tree, 
since  it  prevents  the  entrance  of  water,  fungi  and 
other  agents  of  decay.  If,  however,  the  cut  surface 
is  large,  it  should  always  be  painted  over,  to  preserve 
it  until  the  comparatively  slow  growth  of  the  callus 
covers  it.  (It  may  also  be  remarked  that  a  branch 
should  always  be  cut  off  close  to  the  tree  and  not  at 
a  distance  from  it.)  Pruning  is  the  method  by  which 
man  regulates  the  struggle  among  the  branches  for 
his  own  ends,  and  is  a  study  by  itself;  to  prune 
properly  requires  a  careful  study  both  of  the  indi- 
vidual plant  and  its  surroundings.    Pruning  is  a  fasci- 

1  See  Hunu  aud  Bailey:  "The  Practical  Garden  Book,"  p.  84. 


264  EXPERIMENTS    WITH  PLANTS 

nating  study.  Find  out  all  you  can  about  it  and  the 
principles  underlying  it.^ 

The  form  and  arrangement  of  the  branches  deter- 
mine the  "habit"  of  a  plant,  by  which  we  recognize 
it  even  at  a  distance;  the  object  of  this  arrangement 
is  to  spread  out  the  leaves  in  the  best  possible  fashion 
for  their  work,  with  the  least  expenditure  of  material 
for  construction.  What  plants  do  you  think  have  the 
most  advantageous  habit?  How  many  distinct  kinds 
of  habit  can  you  distinguish? 

What  controls  the  habit  of  the  plant?  As  we 
have  already  learned,  the  main  stem  grows  upward 
in  response  to  the  influence  of  gravity.  Do  the 
branches,  especially  the  horizontal  ones,  assume  their 
positions  in  response  to  the  influence  of  gravity  ?  Notice 
whether  the  tip  of  a  growing  branch  points  in  the 
same  direction  as  the  branch  itself.  If  not,  how  is 
the  change  of  direction  effected  ?  Fasten  tips  of  hori- 
zontal branches  in  various  positions,  some  pointing 
upward,  some  downward,  and  if  possible  exclude  the 
light  by  conducting  them  into  boxes  which  can  be 
kept  dark  inside.  This  experiment  is  not  conclusive, 
but  indicates  the  probable  force  at  work.  The  most 
careful  experiments  so  far  made  seem  to  indicate  that 
the  principal  influence  is  gravity. 

Does  light  also  affect  the  direction  of  growth?   Place 

^  See  Bailey:  "The  Pruning  Book";  also  articles  in  the  Year-Book  of  the 
U.  S.  Department  of  Agriculture  for  1895  by  Woods;  for  1896  by  Webber  and 
Loderaan:  for  1898  by  Saunders;  for  1902  by  Powell. 


TEE    WOBK   OF  STEMS 


265 


potted  plants  (especially  seedlings  of  Grasses,  Radish, 
etc.)  in  a  box  which  admits  light  through  an  opening 
on  one  side  only  (or  shade  the  plants  as  they  grow, 
so  as  to  accomplish  the  same  result) .  The  effect  of 
different  kinds  of  light  may  be  shown  by  covering  the 
opening  with  a  flat  flask  or  bottle  filled  in  one  case 
with  a  solution  of  potassium  bichromate,  in  the  other 
with  ammoniacal  copper  sulphate  (i.  e.,  blue  vitriol 
dissolved  in  water  with  the  addition  of  ammonia  to 
give  a  beautiful  blue  color) .  The  first  transmits  red, 
orange,  yellow  and  a  part  of  the  green  rays;  the 
second  the  rest  of  the  green,  together  with  blue, 
indigo  and  violet  rays. 

As  the  plant  grows  taller  and  develops  a  larger 
crown  of  foliage,  the  stem  is  exposed  to  greater  and 
greater  strains  from  the  action  of  the  wind.  How  to 
secure  the  neces- 
s  a  r  y  strength 
with  the  smallest 
outlay  of  mate- 
rial is  a  problem 
which  we  may 
now  consider.  If 
we  fasten  a  small 
beam  securely  at 
one  end  and  attach  a  weight  to  the  other,  as  shown  in 
Fig.  146,  the  beam  will  tend  to  bend  and  take  the  posi- 
tion  shown    by  the  dotted    lines;    the    upper    surface 


w 


::A. 


ft- 


146.  Diagram  showing 
effect  of  weight  ap- 
plied to  the  end  of  a 


266 


EXPERIMENTS    WITH   PLANTS 


lengthens  and  the  lower  shortens,  while  midway  be- 
tween them,  along  the  line  AB^  there  is  no  tendency 
either  to  lengthen  or  to  shorten.  We  do  not,  therefore, 
need  so  much  material  along  this  line,  and  may  trans- 
fer a  large  part  of  it  to  the  upper  and  lower  surfaces, 

where  the  greatest 


strain  comes.  By 
so  doing  we  make 
a  girder  (Fig.  147) 

147.     Diagram  of  a  girder.  Whlch     COUtaluS   thc 

same  amount  of  material  as  the  beam  but  will  bear  a 
much  greater  load.  On  the  same  principle,  a  hollow 
cylinder  will  bear  a  greater  load  than  a  solid  one  con- 
taining the  same  amount  of  material.  Do  you  find  the 
principle  of  the  girder  and  hollow  cylinder  employed  in 
the  construction  of  the  stem?  On  examining  the  cross- 
section  of  an  herbaceous  stem  under  the  microscope, 
we  find  the  thick-walled  cells  partly  in  the  wood  and 
partly  in  the  strengthening  fibers  (Fig.  131,  str)  which 
may  surround  the  bundle,  as  in  the  Corn^  (Fig.  134,  sir) , 
or  may  lie  external  to  it.  In  all  cases  the  strands  of 
strengthening  fibers  are  connected  with  each  other  or 
with  the  strands  of  wood  by  intervening  tissue  so  that 
they  act  as  the  flanges  of  girders  (see  Fig.  148),  or 
else  they  form   hollow   cylinders  (as  in   Fig.  131).    It 

lit  will  be  noticed  in  the  figure  that,  at  the  sides  of  the  bast  and  there- 
abouts, the  strengthening  fibers  form  only  a  very  narrow  layer,  so  as  not  to 
prevent  the  passage  of  materials  from  the  bast  and  wood  to  the  pith  at 
this  point. 


THI^J     WORJv    OF    STKMS 


267 


148.  Diagram  showing  the  girder- 
like  arrangement  of  strength- 
ening tissues  {str)  in  a  Bulrush 
{Hcirpua). 


will  be  noticed  that  the  thick-walled  cells  are  placed  at 
or  near  the  periphery,  where  the  greatest  strain  comes, 
while   the   center  is   hollow  or 
occupied  by  pith. 

Cut  off  the  head  of  a  stalk 
of  Wheat,  weigh  the  stalk,  and 
find  a  wire  (of  steel,  iron,  cop- 
per, brass,  or,  better  still,  one 
of  each)  of  the.  same  length  as 
the  stalk  and  as  nearly  the 
same  weight  as  possible  ;  at- 
tach the  head  of  Wheat  to  it 
with  a  small  bit  of  sealing-wax 
and  compare  its  rigidity  in  an  upright  position  with 
that  of  the  Wheat- stalk. 

In  the  blade  of  the  leaf  we  find  that  each  vein  is  a 
girder,  or  a  system  of  girders,  and  usually  projects 
from  the  under  side  of  the  leaf  (see  Fig.  149) ,  which 
is  the  best  theoretical  construction. 

In   the   root  we   find   the   woody  cells,    not   at  the 

periphery,  but 
at  the  center 
(Fig. 90).  This 
may  seem  at 
_  first   glance    a 

119.     Cross-section  of  a  Cabbage  leaf  through  the  midrib.       poOr    COUStrUC- 

tion.    When  we   remember,  however,  that   the   strain 
which  comes  upon  the  root  is  a  pulling  strain,  we  see 


268 


EXPEEIMENTS     WITH   PLANTS 


that  the  construction  is  the  best  possible  ;  it  is,  as 
you  can  easil}"  see  by  experimenting  with  a  strand 
composed  of  several  strings  (not  twisted  together), 
the  construction  that  will  stand  the  greatest  pull.  The 
bracing  roots  (above  ground)  of  the  Corn,  which  have 
to  resist  both  thrust  and  pull,  have  strengthening 
tissue  both  at  the  center  and  at  the  periphery. 

In  the  case  of  actively  growing  parts  of  plants  we 
have  a  different  problem,  since  thick,  woody  cells,  like 
those  of  the  wood  and  strengthening  fibers,  would  not 
be  permissible  ;  we  must  have  cells  that  are  highly 
elastic,  so  as  to  be  easily  stretched,  thus  permitting 
v^  y^l  Ib^^  the  growth  of  the  stem  and  yet 
J?^w^  jL  )L^  rigid  enough  to  give  stiffness. 
The  strengthening  tissues  of 
^(  ,v  A_>-%x/  iry  this  part  of  the  stem  (called  the 
-^J^^^^Ck)       yfe=sl      coUenchyma,    Fig.    150)    have 

these  properties ;  they  are  com- 
posed of  cells  thickened  at  the 
150.  CoUenchyma.  comcrs  ouly ;   they  are  able  to 

grow  T3y  absorbing  nutriment  through  the  thin  places 
in  their  walls,  and  so  keep  pace  with  the  growth  of  the 
stem.  The  rigidity  of  the  growing  parts  is  helped  by 
the  fact  that  the  pith  and  internal  tissues  are  com- 
pressed by  the  outer  ones,  which  grow  more  slowly, 
and  so  set  up  strains  (just  as  a  spiral  spring  is  more 
rigid  if  placed  in  a  cloth  bag  which  is  too  small  for  it) . 
Cut  from  the  tip  of  a  growing  Elder  stem  (or  stem  of 


THE    WORK  OF   STEMS  269 

Grape  Vine,  Corn,  Sunflower,  Corn-stalk  or  any  pithy 
stem)  a  piece  at  least  a  foot  long,  carefully  remove  a 
thin  slice  from  the  outer  part  of  the  stem  and  place  it 
in  water  ;  trim  away  everything  from  the  pith,  take  a 
slice  from  it  and  place  it  in  water  beside  the  other. 
Both  slices  must  be  the  full  length  of  the  piece  of 
stem.  Keep  both  slices  under  water,  and  examine  at 
the  end  of  twenty -four  hours.  Which  has  grown  the 
more  I  A  further  illustration  of  this  inequality  of 
growth  may  be  had  by  splitting  a  Dandelion  stalk 
(see  Fig.  152)  lengthwise  into  four  pieces  and  placing 
in  water  (other  pithy  or  succulent  stems  or  stalks 
may  be  treated  in  the  same  way) . 

The  rigidity  of  the  tip  of  the  stem  is  also  largely 
due  to  the  fact  that  the  cells  are  filled  with  water 
under  pressure  (just  as  in  the  case  of  the  root -hair, 
see  page  123),  which  renders  them  rigid.  Cut  off  the 
tip  of  an  herbaceous  stem  two  or  three  inches  in 
length,  place  it  in  a  strong  solution  of  salt  or  sugar 
for  an  hour  or  so.  Explain  the  result.  Place  a  wilted 
stem  in  the  apparatus  shown  in  Fig.  140  or  141, 
and  force  water  into  it  under  pressure. 

As  a  result  of  all  these  devices,  the  herbaceous 
stem  is  a  model  of  strength,  lightness  and  elasticity, 
serving  its  purpose  perfectly;  and  we  may  say  that 
this  problem  has  been  exceedingly  well  solved.  In 
the  case  of  tree  trunks,  the  mere  accumulation  of 
woody  material  provides  the  necessary  sti'ength;  while 


270  EXPERIMENTS    WITH   PLANTS 

in  water-plants  there  is  no  problem  of  this  sort,  since 
the  water  supports  them,  and  consequently  we  find 
them  almost  destitute  of  woody  fiber. 

What  plants  get  their  leaves  up  into  the  sunlight 
with  the  greatest  rapidity  and  the  least  outlay  of 
material?  Consider  the  twining  and  climbing  plants  in 
this  connection  (see  Fig.  151) .  The  problem  of  climb- 
ing is  one  that  has  been  solved  by  various  plants  in 
a  great  number  of  different  ways,  so  that  it  would 
hardly  seem  possible  to  suggest  other  solutions  than 
those  actually  found  in  nature. 

Beginning  with  the  simplest  cases,  we  have  what 
we  may  call  weaving  'plants^  which  weave  themselves 
in  and  out  among  the  branches  of  other  plants  and 
cling  by  means  of  their  branches  and  straight  or 
slightly  curved  leaf -stalks  or  by  means  of  hooks, 
spines,  etc.  As  examples  of  this  class  of  climbers, 
study  the  climbing  Roses,  Blackberry,  Raspberry, 
Jasmine,  etc.  How  does  the  plant  behave  when  it  first 
starts  up  from  the  ground  ?  Where  does  it  begin  to 
branch  !  How  does  it  reach  or  find  the  support  ?  How 
does  it  cling  to  it?  Does  it  always  prevent  its  leaves 
from  being  shaded  by  the  plant  which  supports  it ! 
Do  you  think  that  its  stem  seeks  the  light  ? 

More  special  and  elaborate  adaptations  for  climbing 
are  found  in  tendril -hearing  plants.  The  leaf -stalk  in 
many  cases  acts  as  a  tendril,  as  in  the  Nasturtium, 
Clematis  and  the  Potato  vine;  in  other  cases  the  leaf- 


151.     Clemiitis  uu  an  evergreen  (iu  Califuriiij 
advantage  of  a  climbing  habit. 


272  EXPERIMENTS     WITH   PLANTS 

blade,  either  in  whole  or  in  part,  becomes  transformed 
into  a  tendril,  as  in  the  Pea  family  ;  in  still  other 
eases  it  is  a  branch  which  becomes  a  tendril  (as  shown 
by  its  position  and  development,  or  by  the  fact  that 
it  may  occasionally  bear  leaves),  as  in  the  Squash, 
Pumpkin,  Grrape-vine  and  Passion  Flower.  The  last- 
mentioned  plants  have  tendrils  which  are  especially 
suitable  for  study.  Find  out  all  you  can  about  the 
development  of  the  tendrils  and  their  behavior. 
Does  the  tendril  always  grow  out  straight  at  first  ? 
How  large  must  it  be  before  it  becomes  sensitive  to 
contact  ?  Does  the  tendril  tend  to  swing  around  in  a 
circle,  as  if  seeking  a  support?  How  long  does  it  take 
to  make  a  complete  circle?  Does  this  depend  some- 
what on  the  temperature?  Does  this  movement  seem 
to  be  performed  by  the  tendril  or  by  the  stem  on 
which  it  is  borne  ?  How  soon  does  the  tendril  coil 
after  finding  a  support?  Sticks  of  w^ood  about  the 
thickness  of  a  lead  -  pencil  fastened  to  upright  pieces 
by  a  single  nail  so  that  they  may  be  set  at  any  angle 
are  very  convenient  for  experiments  of  this  kind. 
The  upright  piece  (a  lath  or  portion  of  one)  should 
be  sharpened  so  as  to  be  easily  set  in  the  ground. 
Is  the  tendril  everywhere  equally  sensitive  ?  Can  the 
tendril  coil  equally  well  regardless  of  the  angle  at 
which  the  support  is  set  I  How  does  it  behave  when 
the  support  is  too  large  for  it  to  coil  around  ?  Do 
rain  -  drops  falling   on    the    tendril   cause    it    to   coil  I 


THE    WORK   OF   STEMS  273 

A  part  of  the  shoot  may  be  brought  indoors  and 
placed  with  the  cut  end  in  water,  while  a  stream  of 
water  from  the  faucet  is  directed  on  it.  Do  you  see 
any  advantage  in  this  behavior  of  tendrils  ?  Does 
the  part  of  the  tendril  between  the  stem  and  the 
support  coil  ;  if  so,  in  what  direction  %  Do  you  see 
any  advantage  in  this  coiling  I  Do  the  tendrils  which 
find  support  grow  stronger  and  more  woody  than 
those  which  do  not  ?  What  is  the  advantage  of  this  I 
Why  does  the  tendril  coil?  The  best  answer  we 
can  give  to  this  question  at  present  is  that  contact 
with  a  solid  body  arrests  the  growth  of  the  contact 
side  and  promotes  that  of  the  opposite  side.  Why 
this  is  so  we  do  not  know.  If  we  imitate  the  coiling  of 
a  tendril   by  cutting  out   a  strip   three  or  four  inches 


152.     Behavior  of  a  strip  of  liower-stalk  of  Dandelion,  fastened  at  both  ends  and 
immersed  in  water  (to  show  the  reversal  of  coiling  which  occurs  in  tendrils). 

long  from  a  Dandelion  stalk  (Fig.  152)  and  fastening 
the  two  ends  by  clothes-pins,  we  find  on  putting  it  in 
water  that  it  shows  the  same  reversal  of  the  coils 
which  is  shown  by  a  tendril  which  has  fastened  itself 
to  a  support ;  it  would  seem  that  the  reversal  of  the 
direction  of  the  coiling  is  due  to  purely  mechanical 
reasons,  since  the  same  result  can  be  gotten  with  a 
twisted  string. 


274  JlJXPJfJJilJIJiWTS     WITH    FLAXTS 

Study  also  the  tendrils  of  the  Virginia  Creeper  or 
of  the  Boston  Ivy  (sometimes  called  Japanese  Ivy). 
Why  do  they  grow  toward  the  wall  I  Bend  back  the 
tip  of  the  vine  so  that  the  tendrils  are  directed  away 
from  the  wall,  and  fasten  it  in  this  position.  How 
do  the  tendrils  (especially  the  newly  formed  ones) 
behave  ?  Is  this  due  to  the  light  ?  Conduct  some  of 
the  growing  tips  into  boxes  fastened  on  or  near  the 
wall,  so  that  you  can  control  the  direction  of  the  light 
as  you  please  or  exclude  it  altogether  (if  the  plants 
are  growing  on  a  brick  or  stone  wall  the  boxes  may 
be  simply  wired  to  nails  driven  into  the  mortar  be- 
tween the  bricks  or  stones).  How  do  the  tips  of  the 
tendrils  behave  on  touching  the  wall  I  If  the  little 
cushions  by  which  the  tendril  attaches  itself  be  in- 
jured or  removed,  can  the  tendril  replace  them? 
How  long  does  it  take  a  branch  of  the  tendril  to 
attach  itself  firmly?  How  much  weight  does  it  take 
to  tear  it  loose  when  it  has  firmly  attached  itself? 
Attach  a  small  box  to  it  and  pour  shot  into  it  until 
the  tendril  breaks  loose  from  the  support. 

In  what  direction  do  the  main  stem  and  the 
branches  of  these  plants  grow  ?  Is  this  direction  due 
to  gravity?  Bend  back  and  fasten  some  of  the  tips 
(of  both  main  stems  and  branches)  in  a  horizontal 
position  and  also  pointing  downward.  Is  the  growth 
of  the  stem  affected  by  light?  Experiment  on  the 
stems  by  changing  the  direction  of  the  light  and  by 


THE    WORK   OF   STEMS 


:^/D 


excluding   it   altogether.     Can   you   now  explain   why 
the  tips  of   the  st^ms  press   themselves  to  the  wall? 

How  do  the  main  stem  and  branches  behave  when 
they  reach  the  top  of  a  wall?  How  do  they  behave 
when  unable  to  attach  themselves? 

The  English  Ivy  climbs  in  the  same  manner  as 
the  Boston  Ivy,  but  attaches  itself  by  roots  (Fig.  153) 
instead  of  by  tendrils.  Study  its  behavior 
carefully. 

The  most  interesting  adaptations  for 
climbing  are  found  in  the  twining  plants. 
The  Morning-glory,  Bindweed,  Hop, 
Scarlet  Runner,  Pole  Bean  (or  String 
Bean),  Lima  Bean  or  Sweet  Potato  may 
be  studied  as  examples  of  this  class  of 
plants.  How  does  the  stem  grow  at  first  ? 
When  does  the  tip  begin  to  droop?  Does 
it  appear  to  swing  around  in  a  circle  as 
if  seeking  a  support  ?  As  you  look  down 
on  the  stem  from  above,  does  the  tip 
move  like  the  hands  of  a  watch  (clock- 
wise) or  in  the  opposite  direction  (counter- 
clockwise)? How  large  is  the  circle  de- 
scribed by  the  tip  ?  How  long  does  it  require  to  make 
a  revolution  ?  (Does  the  temperature  affect  the  rate  of 
the  revolution?)  How  does  the  stem  behave  when  it 
meets  a  support  ?  What  is  the  size  of  the  largest  and  the 
smallest  support  it  can  twine  about  ?   Is  it  more  advan- 


Branch  of 
English  Ivy. 


276  EXPEBIMENTS    WITH   PLANTS 

tageous  for  it  to  twine  up  large  stems  or  small  ones  (re- 
member that  it  must,  in  order  to  thrive,  get  its  leaves 
above  those  of  the  plant  on  which  it  twines)?  Does 
it  twine  best  on  a  vertical  or  on  an  inclined  support  ? 
Can  you  see  any  advantage  in  this?  Place  the  sup- 
port on  which  it  is  twining  in  a  horizontal  position; 
how  does  the  plant  behave?  Does  this  make  it  ap- 
pear as  though  gravity  were  a  cause  of  the  twining  ? 
Reverse  a  vertical  support  on  which  the  plant  has 
made  several  turns,  so  that  the  tip  of  the  plant  points 
downward ;  how  does  the  plant  behave  ?  (For  this 
experiment  potted  plants,  with  upright  sticks  set  in 
the  soil  as  supports,  are  very  convenient,  since  it  is 
only  necessary  to  incline  the  pot  or  turn  it  upside 
down.)  Does  light  affect  the  twining?  Keep  the 
plants  in  darkness,  and  observe  the  result. 

Are  the  turns  of  the  stem  equally  steep  at  the  tip 
and  at  the  base  ?  Does  this  arrangement  help  to  hold 
the  plant  in  place  by  causing  it  to  hug  the  support? 
Can  the  plant  twine  as  well  on  a  smooth  support 
(e.  g.,  a  glass  rod)  as  on  a  rough  one  (a  branch  or 
twig)  ?  How  does  the  plant  behave  when  it  reaches 
the  top  of  the  support? 

What  causes  the  plant  to  twine?  The  best  answer 
we  can  give  at  present  to  this  question  is  that  the 
twining  is  due  to  the  influence  of  gravity,  which  stimu- 
lates one  side  to  grow  more  rapidly  than  the  other. 
When  the  tip  points  north  it  is  the  west  side  which  is 


THE    WORK   OF   STUMS  277 

stimulated  in  clockwise  climbers,  the  east  side  in 
counter  -  clockwise  climbers.  Why  gravity  should 
stimulate  the  east  side  rather  than  the  west  (or  vice 
versa)  we  do  not  know,  any  more  than  why  it  should 
stimulate  the  lower  more  than  the  upper  side  in  so 
many  cases. 

Many  plants  have  underground  stems  (e.  g.,  Iris, 
Ferns,  etc.).  Such  stems  are  advantageous  in  many 
ways;  the  plant  may  die  down  in  the  fall  and  come 
up  again  from  these  stems  in  the  spring  (in  such  cases 
food  is  stored  in  them  [Potato,  etc.]  which  enables 
the  plant  to  get  a  good  start  in  the  spring) ;  they 
enable  the  plant  to  spread  and  take  slow  but  sure 
possession  of  a  great  area  (e.  g.,  Horse-tail,  Mints, 
Grasses,  etc.);  they  are  indispensable  to  the  plant 
in  sand-dunes  and  similar  places,  since  they  bind  the 
soil  together  and  keep  it  from  blowing  away.^  It  is 
interesting  to  note  that  these  underground  stems, 
whose  work  is  similar  to  that  of  the  roots,  closely 
resemble  roots  in  their  general  appearance  and  are 
commonly  mistaken  for  them.  This  affords  another 
illustration  of  the  fact  that  function  determines  form 
and  structure.  If  we  force  underground  stems  to  grow 
up  into  the  light  and  air,  they  begin  to  function  like 
ordinary  stems  and  assume,  in  a  measure,  the  ordinary 
appearance  and  structure  of  stems. 

^  Plants  which  have  this  habit  ai-e  of  great  importance  for  binding  the  soil 
of  dikes,  levees,  banks  of  canals,  etc. 


278  EXPEEIMJ^NTS     ]VITH    PLANTS 

The  intimate  connection  between  the  work  of  the 
stem  and  that  of  the  leaf,  which  we  have  had  occasion 
to  note  frequently  in  this  chapter,  is  further  empha- 
sized by  the  fact  that  in  most  cases  the  stem  (in  the 
younger  portions  at  least)  contains  chlorophyll  and 
shares  in  the  work  of  starch-making. 

Does  the  stem  use  up  oxygen  and  produce  carbon 
dioxide,  as  germinating  seeds,  roots  and  leaves  do? 
Repeat  the  experiment  described  on  page  194,  using 
pieces  of  stems  instead  of  leaves. 

How  does  the  stem  obtain  the  necessary  supply  of 
air  for  these  processes?  Do  you  find  stomata  in  the 
epidermis  ? 

Strip  off  a  piece  of  the  epidermis  and  examine  it 
for  stomata  (as  described  on  page  196).  Examine 
also  a  thin  section  in  water,  and  observe  the  bubbles 
of  air  between  the  cells  (under  the  microscope  they 
have  a  very  characteristic  dark  appearance).  Ex- 
amine an  older  part  of  the  stem  (where  the  color  is 
no  longer  green)  in  the  same  way.  Attach  a  bicycle 
pump  to  the  stem  by  a  short  section  of  thick,  white 
rubber  tubing  (which  should  be  secured  at  the  joints 
by  elastic  bands  or  wire),  close  the  free  end  of  the 
stem  with  sealing-wax,  place  the  stem  under  water 
and  pump  air  into  it  (Fig.  154).  The  openings, 
which  are  visible  to  the  naked  eye  and  which  (in  the 
Birch,  Cherry,  etc.)  may  become  an  inch  or  more 
long,  are  known  as  lenticels.    A   section  through  one 


THE    WOBK  OF   STEMS 


279 


of  them  (Fig.  135,  I)  shows  that  it  consists  of  a  mass 

of  loose   cells   which   by  their  growth   have  ruptured 

the  epidermis.    This  process  always  begins  under  one 

of  the   stomata,  and  a  greatly 

enlarged  opening  is  formed  by 

tearing.    The  figure  also  shows 

that  a  layer  of  cork  has  been 

formed  under  the  epidermis ;  it 

is   this  which  gives  the  brown 

color  to  the  stem.    The  cork  is 

a  necessary    protection   to   the 

stem,  for,  as  it  grows  older,  the 

epidermis  falls   off.    When  the 

stem  gets   still  older   the   hark 

is  formed;    this   consists   of    a 

mixture  of  cork,  strengthening  cells  and  the  dead  cells 

of  the  bast.    The  growth  of  the  stem  causes  the  bark 

to  split  and  fissure,  thus  allowing  air  to  enter. 

The  lenticels  are  very  clearly  shown  by  sealing 
both  ends  of  a  short  piece  of  stem  with  sealing-wax, 
placing  it  under  water  in  the  air-pump  and  exhaust- 
ing. In  some  cases  merely  placing  the  stem  in  hot 
water  suffices. 

In  order  to  see  how  readily  air  may  travel  down 
from  the  leaf  into  the  stem,  we  may  fix  a  leaf  air- 
tight in  a  rubber  stopper  (as  described  on  page  205), 
and  fix  this  in  a  tul)e  to  which  we  fit  a  piston  (con- 
structed as  described  on  page  188) ;  pour  in  a  little 


154.  Method  of  investigating  lenti- 
cels (air  is  pumped  into  the  sub- 
merged stem  by  means  of  the 
bicycle  pump). 


280 


EXPERIMENTS    WITH  PLANTS 


155.  Method  of  investigating 
the  entrance  of  air  into  the 
stem  by  way  of  the  stomata. 


water  and  exhaust  the  air  (Fig. 
155).  Leaves  of  Geranium,  Mag- 
nolia, Laurel,  etc.,  may  be  recom- 
mended for  this  experiment. 

Having  tried  this  experiment, 
perform  the  following:  Fix  a  leaf 
or  leafy  branch  air-tight  in  a  cork 
and  insert  the  latter  into  a  bot- 
tle brimful  of  water  so  as  to  ex- 
clude air  as  much  as  possible  (it 
will  be  necessary  to  insert  the 
point  of  a  knife  beside  the  cork 
to  let  the  water  escape).  Hang 
up  the  bottle  in  the  sunlight 
(Fig.  156).  The  transpiration  of 
the  leaves  will  withdraw  water 
from  the  bottle,  causing  a  partial 
vacuum,  with  the  result  that  air 
will  be  drawn  in  through  the 
leaves  and  rise  in  bubbles  from 
the  cut  end  of  the  stem.  The  ex- 
periment shows  clearly  that  the 
air  and  the  water  travel  in  differ- 
ent channels  in  the  stem,  so  that 
they  do  not  interfere  with  one 
another. 

In  order  to  test  how  far  the 
air  penetrates  and  where  it  travels 


THE    WORK  OF  STEMS 


281 


I 


in  the  stem,  fix  a  short  piece  of   stem  air-tight  in  a 

cork   and   fit  this    in   a   lamp-chimney  (as   shown  in 

Fig    139).    Pour  in  water,   and 

exhaust.    Or  force   air   through 

the    stem    by    an    arrangement 

similar  to    that   shown    in  Fig. 

141,  in  which  case  we  may  ob- 
serve   with    a    hand  -  lens    just 

where  the  air  issues. 

It  sometimes  happens  that  in 

coating  trees  with  tar  to  protect 

them    from   insects    and    fungi, 

they    suffer    severely   from    too 

liberal     an     application,    wdiich 

deprives  the  stem  of  air. 

To  determine  the  effect  of  ex- 
cluding air  from  the  stem,  we  may  take 
Willow  cuttings  and  suspend  them  in 
moist  air  (see  Fig.  157),  by  attaching 
them  to  a  cork  fitted  into  a  lamp- 
chimney  which  stands  in  water.  As  the 
experiment  is  to  last  for  several  weeks, 
the  constant  level  apparatus  described 
on  page  27  (Fig.  27)  may  be  used. 
Let  some  of  the  cuttings  be  completely 
smeared  over  with  vaseline,  so  as  to  en- 

157.   Willow  twig      tirely  exclude  air.    Place  all  the  cuttings 

STispendea     in     a  •'  *-• 

saturated  atmos-      ^^^^^^  favorable  couditions  of  growth. 


156.  Method  of  investigating  the 
entrance  of  air  into  the  stem 
by  way  of  the  stomata  and 
leuticels. 


282  EXPERIMENTS    WITH  PLANTS 

When  the  untreated  cuttings  have  put  forth  vigor- 
ous shoots,  those  with  vaseline  on  them  will  probably 
show  little  or  no  development  of  shoots.  Now  care- 
fully wipe  off  the  vaseline  with  a  rag,-  and  then  rub 
the  stems  well  with  dry  sand  and  place  them  again  in 
the  chimney  or  set  them  in  water,  to  see  if  they 
will  grow. 

Cuttings  and  seeds  sent  long  distances,  especially 
to  or  from  the  tropics,  are  frequently  ruined  by  start- 
ing to  grow  prematurely  in  transit.  Of  the  three  fac- 
tors which  promote  growth,  namely,  moisture,  warmth 
and  air- supply,  the  attempt  is  constantly  made  to 
control  the  first  two,  which  is  in  most  cases  difficult 
or  impossible,  while  the  control  of  the  air- supply, 
although"  easily  accomplished,  has  been  neglected. 
Sealing  up  the  plants  in  air-tight  tins  or  packages 
has  been  tried,  but  this  is  far  less  effective  than  seal- 
ing each  cutting  by  means  of  wax,  paraffin  or  similar 
substances.  This  seems  to  promise  a  favorable  field 
for  experiment. 

How  do  the  submerged  portions  of  water-plants 
get  air?  When  they  have  leaves  which  project  above 
the  water  or  float  on  its  surface,  they  may  receive  a 
supply  of  air  through  them.  Examine  some  plants  of 
this  sort  (e.  g.,  Pond  Lilies,  Arrowhead,  etc.),  and 
notice  what  enormous  air- passages  exist  in  them.  Do 
these  passages  extend  up  into  the  leaves?  Examine 
also  swamp  plants  which  have  their  roots  in  water  or 


THE    WORK   OF   STEMS 


283 


mud.  In  the  case  of  plants  which  live  entirely  sub- 
merged it  would  seem  that  they  must  get  their  air 
from  the  water.  Does  water  contain  air?  We  have 
already  gained  some  evidence  on  this  point  in  our 
previous  experiments.  Place  some  tap-  or  spring - 
water  in  the  air-pump,  and  exhaust.  Are  air- bubbles 
formed!  Boil  some  of  the  water  for  half  an  hour, 
allow  it  to  cool,  place  it  in  the  air-pump,  and  exhaust. 
Are  bubbles  formed  to  the  same  extent  as  before  ? 
Careful  tests  have  shown  that  water  may  dissolve  a 
large  amount  of  air.  It  is  this  dissolved  air  in  the 
water  on  which  totally  submerged 
plants  depend  for  their  supply. 

In  order  to  grow  water-plants 
successfully  in  aquaria,  it  is  fre- 
quently necessary  to  furnish  them 
with  a  constant  supply  of  air.  This 
may  be  done  by  means  of  the  ap- 
paratus shown  in  Fig.  158.  It  con- 
sists of  a  long,  vertical  glass  tube 
about  one-eighth  inch  in  diameter, 
widened  a  little  at  the  top.  When 
a  drop  of  water  falls  into  this 
from  the  siphon  it  will,  if  it 
strikes   in   the   center,  fill   the 

158.  Apparatus  for  supplying  air  in  a 
tube    and  then  fall   down,   carry-  constant  stream  to  an  aquarluna. 

ing  the  air  before  it  (i.  e.,  it  acts  like  a  piston).    On 
arriving  at  the  T-tube  connection,  the  air  passes  over 


284 


EXPEMIMEJSTS    WITH   PLANTS 


into  the  aquarium,  while  the  water  falls  straight  down 
into  a  receptacle  below.  The  water  outlet  tube  must 
dip  a  little  deeper  under  water  than  the  air  outlet 
tube  ;  otherwise  the  air,  following  the  path  of  least 
resistance,  will  escape  by  the  same  outlet  as  the  water. 
In  order  to  keep  the  latter  submerged  to  a  constant 
depth,  use  a  small  jar  as  shown  in  the  figure  :  the 
shallow^er  the  depth  the  greater  the  amount  of  air  which 
will  pass  over,  since  enough  drops  must  accumulate 
in  the  tube  to  overcome  the  pressure  of  the  water  at 
the  outlet  where  it  escapes.  The  drops  should  be  made 
as  large  as  possible  and  should  strike  the  tube  nearly 
in  the  center ;  if  the  bore  of  the  tube  is  too  large  the 
drop  will  not  fill  the  cross -section  and  consequently 
will  not  act  as  a  piston.    In  order  to  regulate  the  rate 

of  flow  of  the  siphon,  it  may  be 
drawn  out  to  a  fine  point  (as 
shown  in  the  figure),  which  can 
be  broken  off  to  the  requisite 
degree  and  covered  with  cotton 
(held  in  place  by  an  elastic 
band)  to  filter  the  water. 
A  very  successful  way  of  growing  algae  and  other 
water-plants  is  shown  in  Fig.  159.  A  jar  or  bottle  is 
filled  with  water  and  inverted  over  water :  carbon 
dioxide  is  conducted  into  it  from  a  bottle  containing 
fragments  of  marble  (or  marble  dust  or  whiting),  into 
which  we  slowly  pour  weak  sulphuric  acid  by  means  of 


.  Arrangement  for  supplj-inK 
carbon  dioxide  to  plants 
growing  in  water. 


THE    WORK   OF   STEMS  285 

a  funnel  passing  through  the  cork :  a  tube  passing 
through  the  cork  serves  to  conduct  the  carbon  dioxide 
into  the  jar.  A  few  moments  must  be  allowed  for  the 
carbon  dioxide  to  drive  the  air  out  of  the  bottle  and 
tube;  the  tube  should  then  be  introduced  into  the  jar 
and  the  evolution  of  gas  continued  until  the  jar  is 
nearly  filled  with  gas. 

Another  method  is  to 
grow  the  algse  in  small  tubs 
(of  wood  fiber)  filled  with 
water,  keeping  a  huge  bub- 
ble of  carbon  dioxide  or  air     ^^^^.t^Tn^^St^^iSTb^^^^^^^^^ 

just     below,    them,     as     shown  carbon  dioxide  or  air. 

in  Fig.  160.  This  bubble  is  kept  in  place  by  means 
of  a  net  (made  of  cheese-cloth  or  mosquito  netting)  at- 
tached to  a  cii'cular  hoop  of  small  flexible  lead-pipe  (^), 
which  rests  on  the  bottom  of  the  tub.  The  bubble  may 
consist  of  air,  or  air  blown  from  the  lungs,  or  of  carbon 
dioxide  generated  in  the  apparatus-  shown  in  Fig.  159. 
The  common  method  of  placing  aquatic  animals  and 
insects  and  aquaria  in  order  to  supply  carbon  dioxide 
is  excluded  for  our  purpose,  for  the  reason  that  they 
feed  on  the  algae.  We  may,  however,  place  a  well- 
developed  cutting  of  Willow  or  Wandering  Jew  (Fig. 
84)  in  the  jar  ;  the  carbon  dioxide  excreted  from  its 
roots  will  be  a  great  stimulus  to  the  algsB. 


CHAPTER   VI 
THE  WORK  OF   FLOWERS 

In  preparation  for  flowering,  the  plant  stores  up  a 
supply  of  food.  How  long  does  this  take;  what  kind 
of  food  is  stored,  and  where?  Compare  the  behavior, 
in  this  respect,  of  plants  which  live  for  a  year  only 
(annuals),  plants  which  live  two  years  (biennials)  and 
plants  which  live  on  from  year  to  year  (perenuials). 
Which  method  of  preparation  for  flowering  seems  to 
you  in  general  most  effective  I  Find  out  what  you  can 
about  the  behavior  of  Cacti  and  the  Century  Plant. 
Study  especially  the  different  kinds  of  bulbous  plants. 
Cut  open  the  bulb  of  a  Hyacinth,  and  notice  the  food 
stored  for  next  spring's  growth,  and  the  flowers 
already  formed  and  prepared  to  open  at  the  earliest 
opportunity. 

The  formation  of  flower -buds  during  the  previous 
season  would  seem  to  be  an  advantage.  Does  this 
occur  in  most  plants  ?  Open,  and  examine  with  a 
hand-lens  the  large  winter-buds  of  the  Horse-Chestnut, 
Buckeye,  Hickory,  Maple,  Poplar,  etc.  Can  you  find 
any  traces  of  flowers?  In  some  cases  the  flower- buds 
may   be   recognized   by   their   position  ;    for  example, 

(286) 


THU    WOBK    OF   F LOWERS  287 

some  Plums  have  a  flower- bud  on  each  side  of  the 
leaf- bud.  As  the  new  leaves  come  out  in  the  spring, 
we  find  the  three  buds  already  formed  in  the  axil  of 
ea.ch  leaf,  and  the  flowers  which  are  soon  formed 
inside  the  flower- buds  must  wait  a  full  year  before 
opening.  In  the  first  stages  of  their  formation  the 
flowers  may  be  too  small  to  be  seen  (except  with  the 
microscope) ;  we  must  not,  therefore,  be  hasty  in  con- 
cluding that  they  are  not  yet  present  in  any  given 
case.  Fruit  -  growers  have  thought  it  desirable  to 
know  the  exact  time  when  the  flowers  were  formed  in 
the  bud,  in  order  that  they  might  try  to  control  this 
process  by  irrigating  and  applying  special  fertilizers 
at  the  proper  time.  Learn  what  you  can  about  these 
points . 

Examine  some  flower- buds  which  are  just  open- 
ing. Do  you  find  an  abundance  of  food  in  them  and  in 
the  stems  on  which  they  are  borne  ?  What  kind  of 
food  predominates  ?  Is  there  a  rapid  consumption  of 
food  by  the  developing  flowers  f  Repeat  the  experi- 
ment described  on  page  34,  using  flower- buds  instead 
of  seeds.  (Buds  of  Composite  flowers,  e.g..  Sunflower, 
Dandelion,  Daisy,  etc.,  are  especially  good.)  What 
does  the  result  signify  ?  Can  you  detect  any  setting 
free  of  heat  in  the  developing  buds  (see  page  36)  ? 

Of  what  use  is  the  calyx,  or  green  covering,  of  the 
flower-bud  ?  We  may  endeavor  to  answer  this  question 
by  removing   the  calyx  from    the  bud   at  as   early  a 


288  EXPERIMENTS    WITH  PLANTS 

stage  as  possible  in  its  development.  The  Passion 
Flower,  Bindweed,  CobsBa  and  other  flowers  where 
the  calyx  is  large  and  inflated  are  especially  well 
adapted  to  such  experiments,  but  any  large  flower, 
such  as  the  Poppy,  Rose,  etc.,  may  be  chosen.  Re- 
move the  calyx  while  the  bud  is  still  quite  small, 
taking  care  not  to  injure  the  petals  or  other  parts  of 
the  flower.  It  seems  natural  to  suppose  that  the  calyx 
protects  the  flower- bud  against  drying  in  the  same 
way  that  the  bud- scales  protect  the  leaf- bud.  What 
does  the  experiment  show  in  regard  to  thisf  Since  pet- 
als are  more  easily  injured  than  leaves  by  rain,  frost, 
etc.,  even  when  the  calyx  is  not  removed,  we  should 
keep  sharp  watch  to  see  whether  the  flowers  deprived 
of  calyx  suffer  more  than  the  controls  in  these  respects. 
Do  you  find  that  flowers  which  have  been  deprived 
of  the  calyx  are  able  to  develop  normally?  Does  the 
sTKifMA  result  depend  on  how  early 

the  calyx  is  removed? 

Let  us  now  look  at  the 

interior  of  the  flower.    If 

we  cut  open  flowers  of  the 

,«i    n>,      V,  .        .    ^.         Cherry,  as  shown  in  Fig. 

161.    Cherry  blossom  cut  open,  to  snow  •^  '  <=' 

the  parts  of  the  flower,  161^  WC  fiud  thC  SCCd-CaSCS 

(or  ovaries),  containing  the  tiny  seeds  (or  ovules). 
Surrounding  the  ovary  are  the  anthers,  or  pollen-cases, 
mounted  on  short  stalks,  and  containing  a  yellow  dust, 
the  pollen. 


THE    WOBK    OF  FLOWERS  289 

When  the  pollen  is  fully  formed,  the  anthers  open 
and  allow  it  to  escape.  Of  what  use  is  the  pollen?  To 
answer  this  question,  we  may  deprive  the  flower  of 
pollen.  For  this  purpose,  choose  flowers  which  are 
large  enough  to  permit  of  the  necessary  manipulation; 
select  unopened  buds;  carefully  open  them  at  the  tip, 
and  remove  the  anthers  with  a  forceps,  taking  care  not 
to  injure  the  other  parts  of  the  flower.  The  flower  is 
now  deprived  of  all  its  pollen;  but  more  pollen  may  be 
easily  brought  from  neighboring  flowers  by  the  wind  or 
by  the  bees  (and  other  insects),  which  constantly  fly 
from  flower  to  flower.  To  prevent  this,  we  may  protect 
the  flowers  by  covering  them  with  small  paper  bags 
tied  tightly  on  the  stalk,  so  as  to  completely  enclose 
the  flower.  Do  flowers  so  treated  form  fruit!  We 
must,  in  every  case,  have  controls  which  set  fruit, 
in  order  that  we  may  know  whether  the  experimental 
conditions   are  responsible  for  the  lack  of  it. 

If  the  pollen  is  necessary  for  fruit -making  we  may 
next  ask.  How  does  it  operate?  We  can  see  this  most 
clearly  if  we  examine  the  flower  of  some  Grass  or 
Grain.  (Timothy  is  best  for  this  purpose.)  Examining 
a  flower  whose  anthers  have  withered,  we  see  what 
appears  to  be  a  tiny  brush  projecting  from  the 
flower.  On  removing  the  outer  coverings  of  the 
flower  with  needles,  we  see  the  ovary  (seed -case)  with 
two  brush -like  styles  or  stigmas  :  on  examining  with 
a  hand -lens  we  see  that  they  are  covered  with  pollen- 


290  IJXPJ'Jh'fJflJXTS     WITH    PLANTS 

grains.     Fig.  162   shows   the   appearance   of   these   in 

the  Oat. 

Placed    in    a    drop    of   water    on    a    slide,    covered 

with  a  cover- glass  and  examined  under  the  high 
power  of  the  microscope,  many  of  the 
pollen -grains  are  seen  to  be  sending 
out  long  tubes  (Fig.  163)  which  grow 
down  along  the  brush -like  style  to- 
ward the  ovary.  What  happens  after 
that  can  be   seen  only 

162.    Ova^-y'ueed-case)  of     !»     gOOd      SCCtioUS,      but 
Oat  with  feathery  style.       ^^y    \^q    dCSCrlbcd    iu    a 

few  words.  Inside  the  ovary  lies  (as 
you  may  see  with  a  hand -lens)  a  tiny 
seed  or  ovule  (Fig.  161).  Within  this  is 
a  mass  of  tissue,  in  the  central  cavity 
(embryo  sac,  Fig.  164)  of  which  lies  the 
Qgg.  In  the  center  of  the  eg^  is  a 
nucleus.  The  pollen -tube  approaches 
to  within  a  short  distance  of  the  egg 
and  opens  at  the  end;  a  nucleus  issues 
from  it  which  unites  with  the  nucleus  of 
the  Qgg^  so  that  the  two  form  a  single 
nucleus.  The  egg  then  begins  to  develop 
and  eventually  forms  a  tiny  plant,  with  '''•  sf ^Te "o f 'o S 

,.    ,  T     ,  ,  n       T     •  showing    a    pol- 

caulicle  and  leaves,  such  as  we  find  m        len-grain pushing 

out  a   long  tube 

the  ripened  seed.  ^^^\lV"iroik 

Unless  the  union  of  the  nuclei  takes        o^S&lS! 


THE    WOKK    OF   FTjOWEBS 


291 


place,  the  eg^  does  not 
ordinarily  develop; 
hence  we  see  why 
pollen  is  necessary  in 
order  to  set  seed.  If 
we  examine  various 
flowers  with  a  hand- 
lens,  we  find  the  pol- 
len deposited  in  a  par- 
ticular spot,  which  is 
provided  with  brushes, 
hairs  or  sticky  sub- 
stances in  order  to 
retain  it.  This  spot  is 
called  the  stigma  (see 
Fig.  161).  What  hap- 
pens if  we  remove  the 
stigma  ?  Remove  the 
stigma  before  the  bud 
is  open,  being  careful 
not  to  injure  the  other 
parts  of  the  flower. 
Do  not  protect  the 
flowers  from  insects, 
but  rather  assist  pol- 
lination by  placing 
pollen  on  the  flower. 
Do  you  find  that  flow- 


1G4.  Embryo  s;ic  of  ;i  Lily,  showing  the  iinion  of 
the  nucleus  from  the  pollen-tube  {pn)  with  the 
egg(e):  the  second  pollen -tvibe  nu<-leus  (spn) 
xmites  with  two  endosperm  pro  nuclei  {nid), 
which  nniltiply  and  form  the  endosperm:  {ant) 
antipodal  cells,  (nr)  nurse  nuclei  which  help 
nurish  the  egg,  etc.,  {p)  pollen-tube. 


292  EXPERIMENTS    WITH  PLANTS 

ers  so  treated  are  able  to  set  seed?  We  must,  of 
course,  have  unmutilated  flowers  (if  possible  on  the 
same  plant)  for  comparison,  and  it  is  important  that 
we  choose  a  plant  whose  flowers  set  seed  freely. 

The  effectiveness  of  the  stigma  in  retaining  pollen 
may  be  tested  by  dusting  the  flower  with  flour  or  any 
white  powder  and  afterward  endeavoring  to  blow  it 
away.  In  the  Monkey- flower  the  stigma  has  two  lips 
which  come  together  and  hold  the  pollen  firmly  when 
it  has  been  deposited.  Touching  the  open  lips  with 
the  point  of  a  pencil  will  cause  them  to  close  at  once. 
The  silk  of  the  Corn  is  practically  a  long  stigma 
covered  with  projections  to  retain  the  pollen,  which  is 
carried  by  the  wind:  Wheat  and  Grasses  generally 
have  such  stigmas,  but  they  are  much  shorter  and  less 
conspicuous  than  in  the  Corn. 

It  is  the  work  of  the  stigma  not  only  to  capture  and 
retain  the  pollen,  but  also  to  provide  favorable  con- 
ditions for  its  germination  and  to  nourish  it  during  the 
growth  of  the  pollen -tube.  The  sticky  substance  on 
the  stigma  contains  sugar  (as  you  can  easily  ascertain 
by  tasting  or  applying  a  chemical  test),  which  serves 
the  germinating  pollen-grain  for  food.  If  we  place 
pollen-graius  in  a  drop  of  sugar  solution  of  the  right 
strength,  we  shall  be  able  to  observe  their  germination, 
which  may,  in  some  cases,  take  place  in  a  few  minutes 
(Willow,  Sweet  Pea).  It  is  advisable  to  make  up  cane 
sugar  solutions  of  35  per  cent,  10  per  cent  and  5  per 


THE    WORK    OF  FLO  WEBS  293 

cent,  and  test  pollen-grains  of  various  species  in  each. 
The  following  may  serve  as  a  guide  :  3  per  cent, 
Tulip,  Narcissus,  Onion;  15  per  cent,  Sweet  Pea, 
Nasturtium  (Indian  Cress) . 

A  very  convenient  method  is  to  take  a  glass  or 
metal  ring,  or  one  cut  out  of  wax  (about  one -half 
inch  in  diameter),  and  cement  it  to  a  glass -slide  with 
vaseline:   on  this  lay  a  cover-glass  from  the  center  of 

\    m     ^^- — T^ — '^ 


\ 


d 

165.    Hanging  drop  arrangement  for  the  cultivation  of  pollen-grains:    («)  slide, 
(c)  cover-glass,  (r)  ring,  {d)  hanging  dx'op.   (Sectional  view.) 

which  hangs  a  drop  of  sugar  solution  containing  the 
pollen  (Fig.  165) ;  seal  this  air-tight  by  means  of 
vaseline. 

In  each  case,  make  control  experiments  by  placing 
some  of  the  pollen  in  rain-water  (tap -water  or  spring- 
water  may  be  used).  In  which  medium  does  it  grow 
best  ?  Vary  the  experiment  by  cutting  off  the  tip  of  the 
stigma  and  placing  it  at  one  edge  of  the  drop.  Do  the 
pollen-grains  show  any  tendency  to  grow  toward  it?^ 
If  so,  it  may  help  us  to  explain  why  the  pollen-tubes 
grow  down  to  the  ovary.  Presumably,  in  such  cases, 
the  stigma  gives  off  substances  which  attract  the  pollen- 

1  The  fact  that  the  pollen  -  tubes  have  a  tendency  to  grow  away  from  the 
air  at  the  ed<?e  of  the  drop  should  be  taken  into  account.  Make  some  ex- 
periments on  this  point,  by  leaving  the  chamber  open  to  the  air  and  also  by 
sealing  it  air-tight  with  vaseline. 


294  EXPERIMENTS    }VJTII  PLANTS 

tubes;  and  we  suppose  that  the  tubes  are  attracted  to 
the  ovules  in  the  same  way. 

The  fact  that  pollen- grains  germinate  or  burst 
when  placed  in  water  shows  the  importance  of  protect- 
ing them  from  rain  and  dew,  since  they  are  not,  when 
germinating,  in  suitable  condition  for  transportation 
(any  more  than  germinating  seeds  would  be)  .^  Notice 
how  quickly  they  dry  up  and  perish  if  exposed  to  dry 
air  while  in  this  condition. 

Do  you  find  devices  to  protect  the  pollen  from  rain  ? 
Examine  as  many  kinds  of  flowers  as  you  can  after  a 
shower,  or  sprinkle  them  with  a  watering-pot  and  note 
the  result.  Here  we  find  so  many  different  ways  of 
solving  the  same  problem  that  it  is  an  interesting 
matter  to  study.  The  flowers  may  be  protected  by  the 
leaves  (Jewelweed,  Linden),  by  the  sepals  (Acanthus), 
by  the  closed  petals  (Pea  family.  Snapdragon),  by 
an  arching  roof  (Violet,  Monkshood),  by  contract- 
ing the  tube  of  the  corolla  above  the  stamens  (Phlox, 
Primrose)  or  by  the  stigma  (Iris).^ 

Many  flowers  grow  in  a  horizontal  position  or  hang 
downward,  which  effectually  prevents  the  entrance  of 
rain.     Others,  which   grow   upright,   assume    a  droop- 

1  The  pollen,  like  the  seed,  varies  greatly  in  the  length  of  time  it  retains  its 
vitality.  Ordinarily  it  will  keep  for  at  least  a  week  in  a  cool,  dry  place,  without 
deterioration.  The  Arabs,  who  gather  the  pollen  of  the  Date  Palm  for  arti- 
ficial pollination,  appear  to  keep  it  for  one  or  even  two  years  without  much 
loss  of  vitality.  See  an  article  by  Swingle  on  the  Date  Palm  in  the  Year  Book 
of  the  U.  S.  Dept.  of  Agriculture  for  1900. 

2  See  Kerner  and  Oliver,  "Natural  History  of  Plants,"  Vol.  H,  p.  104. 


THE    WORK    OF   FLO  WEES  295 

ing  position  on  the  approach  of  rain  (Wood  Anemone, 
Scabious,  Herb  Robert,  Potato,  etc.);  others  accom- 
plish the  same  result  by  closing  the  flower  tightly,  and 
are  useful  as  weather  indicators  (Poor  Man's  Weather- 
glass, Water-lily,  Dandelion,  etc.).  Such  flowers  are 
regularly  closed  during  the  night,  and  thus  the  pollen 
is  protected  from  the  dew.  Many  other  flowers  seem 
to  have  no  means  of  protection,  but  it  will  be  found  in 
many  cases  on  examination  that  the  anthers  them- 
selves close  to  protect  the  pollen  (Plantain,  Grape, 
Castor- bean,  etc.),  or  a  layer  of  hairs  or  a  w^axy 
covering  prevents  the  pollen  from  becoming  wet. 

It  should  be  noted  that  most  of  these  devices  pro- 
tect the  nectar,  or  honey,  equally  with  the  pollen. 

Flowers,  as  a  rule,  open  and  close  quite  regularly 
at  certain  times  of  day:  the  great  Swedish  botanist, 
Linnaeus,  constructed  a  floral  clock  in  which  the  hours 
were  told  by  the  opening  and  closing  of  the  flowers. 
This  naturally  raises  the  question,  Is  the  opening  and 
closing  of  the  flower  due  to  the  action  of  light  ?  Select 
some  flowers  which  open  and  close  quickly,  such  as 
Oxalis,  Dandelion,^  etc.,  and  try  the  effect  of  covering 
them  with  a  box  in  the  middle  of  the  day  or  of  keep- 
ing them  under  a  dark  box  for  two  or  three  days, 
during  which  time  they  should  be  examined  at  inter- 
vals ;  try  to  keep  the  temperature  as  nearly  like  that 

1  Some  flowers  never  open  a  second  time  and  consequently  cannot  be  used 
for  the  experiment. 


296  EXPERIMENTS    WITH  PLANTS 

of  the  controls  as  possible  ;  on  exposing  them  again 
to  the  light,  what  happens  ? 

Temperature,  as  well  as  light,  plays  a  part  in  the 
process.  The  Crocus  or  the  Tulip  can  be  made  to  open 
or  close  at  any  time  of  day  by  changing  the  tem- 
perature. The  experiment  should  be  commenced  in  the 
morning  before  the  flower  has  opened,  and  the  tem- 
perature should  not  go  above  15°  C.  On  placing  it 
where  the  temperature  is  20°  to  25°  C.  it  begins  to 
open:  if  it  be  returned  to  the  original  temperature  it 
will  soon  begin  to  close.  In  this  way  it  is  possible  to 
make  it  open,  close  and  open  again  all  within  an 
hour.^ 

The  flowers  of  some  alpine  plants  have  been  ob- 
served to  open  and  close  several  times  during  the 
course  of  an  hour  as  they  were  illuminated  or  dark- 
ened by  passing  clouds. 

The  amount  of  moisture  in  the  air  also  has  some- 
thing to  do  with  the  matter.  A  flower  of  the  Poor 
Man's  Weather-glass  kept  in  a  saturated  atmosphere 
refuses  to  open  even  when  given  the  normal  amount 
of  illumination.  Make  experiments  on  this  point. 
The  flowers  may  float  on  a  cork  in  a  glass  jar  which 
is  covered  with  a  piece  of  glass  cemented  on  air-tight 
with  vaseline.  (The  jar  should  be  large  enough  so 
that   the    flower  will  not  suffer  for  lack  of  oxygen  : 

»  Simply  submerging  the  flower  in  water  which  is  about  10°  C.  warmer  than 
the  air,  will  in  most  cases  cause  it  to  open  rapidly. 


THE    WORK    OF  FLOWERS  297 

a  few  green  leaves  placed  in  it  will  be  of  great 
assistance  in  this  respect.) 

The  opening  of  the  flower  seems  to  be  caused  by 
more  rapid  growth  of  the  inner  side  of  the  petal; 
the  closing  by  more  rapid  growth  of  the  outer  side  of 
the  petal:  how  far  the  latter  process  would  go  if  the 
other  petals  did  not  hinder  it,  may  be  easily  seen  by 
cutting  them  away. 

It  appears,  then,  that  the  petals  protect  the  pollen 
from  rain  and  dew  ;  we  have  already  found  that  the 
calyx  prevents  the  inner  parts  of  the  flower  from 
drying  up  during  their  development,  and  it  seems 
probable  that  the  petals  serve  the  same  function  also. 
It  would  be  easy  to  determine  this  point  by  a  few 
experiments.  But,  so  far  as  protective  purposes  go,  the 
most  striking  thing  about  the  petals,  i.  e.,  their  color, 
would  seem  to  be  useless.  We  may  therefore  ask,  Of 
what  use  is  the  color  of  the  flower?  It  is  quite  safe  to 
say  that  every  one  has  been  told  that  insects  are 
attracted  to  flowers  by  their  colors.  The  petals,  with 
their  bright  and  showy  colors,  have  been  compared 
to  sign-boards,  which  advertise  to  the  bees  the  pres- 
ence of  the  honey  and  pollen  of  which  they  are  in 
search.  The  insects,  in  their  visits,  carry  pollen  from 
flower  to  flower,  and  so  enable  the  flower  to  set  fruit. 

It  is  true  that  there  exist  a  great  number  of  devices 
for  making  the  flower  conspicuous,  chief  of  which  are 
striking  color  and  the  grouping  of  flowers  in  masses. 


298  EXPERIMENTS    WITH  PLANTS 

SO  that  the  color  is  visible  from  a  distance  (Elder, 
Parsley  family,  etc.).  The  head  of  a  Dandelion  or 
Sunflower  is  such  a  group,  being  made  up  of  numer- 
ous small  flowers,  and  in  the  Sunflower  there  is  aii 
interesting  division  of  labor,  in  that  the  outer  flowers 
are  for  show  only  (producing  no  seed),  while  the 
inner  are  inconspicuous  but  devote  themselves  entirely 
to  seed -bearing.  It  should  be  noted,  morever,  that 
the  contrast  in  color  between  the  black  center  and  the 
yellow  rim  makes  the  flower  much  more  conspicuous 
than  either  color  alone.  Make  an  experiment  on  this 
point  by  covering  the  center  with  the  yellow  petals 
and  then  going  off  some  distance  to  note  the  effect. 
Look  out  for  cases  of  color  contrast,  e.  g.,  contrast 
between  the  flowers  and  the  background  of  leaves, 
between  the  stamens  and  the  petals,  between  the  old 
and  fading  flowers  and  the  young  ones,  etc. 

Notice  flowers  which  are  growing  beside  a  wall  or 
other  screen  which  cuts  off  the  light.  Do  they  turn 
toward  the  light?  Does  this  aid  in  making  them  con- 
spicuous ?  Perform  some  experiments  to  test  their 
sensitiveness  to  the  light.  Study  the  behavior  of  Dan- 
delion, Sunflower  and  Wild  Mustard  flowers,  with 
reference  to  "following  the  sun." 

It  is  said  that  not  only  are  insects  attracted  by  the 
colors  of  flowers,  but  that  they  are  partial  to  certain 
colors.  Bees  are  said  to  prefer  blue  and  violet,  to 
care   little   for  yellow,    and  ,to  avoid   scarlet.     In  my 


THE    WORK    OF    FLOWERS  299 

garden  it  happened  that  Parsnip  and  Chickory  grew 
side  by  side,  the  bhie  flowers  of  the  one  mingling 
with  the  yellow  flowers  of  the  other.  In  this  case 
I  have  watched  with  interest  the  striking  difference 
in  the  behavior  of  bees  and  flies.  The  bees  were 
abundant  on  the  blue  flowers,  but  in  several  hours 
of  watching  not  a  single  bee  was  seen  to  alight  on 
a  yellow  flower,  although  they  would  often  spring 
over  one  to  get  at  the  next  blue  flower.  On  the 
other  hand,  the  yellow  flowers  fairly  swarmed  with 
flies  of  different  species,  while  not  a  single  one  ap- 
peared on  the  blue  flowers. 

We  must  take  into  account,  in  this  connection,  a 
peculiarity  which  the  bee  has  of  visiting,  as  a  rule,  but 
one  kind  of  a  flower  at  a  time.  I  have  often  per- 
formed the  experiment  of  placing  a  branch  of  the 
blue  -  flowered  Thyme  (of  which  the  bees  are  very 
fond)  in  a  bed  of  Yellow  Lupine,  in  which  they  were 
busily  at  work.  They  avoided  the  Thyme  uniformly, 
going  over  it  or  around  it  to  get  at  the  Yellow 
Lupine  flowers.  But,  on  placing  a  cluster  of  Lupine 
flowers  in  a  bed  of  Thyme  blossoms,  they  paid  no 
attention  to  it. 

Flowers  which  display  no  conspicuous  sign -boards 
are,  nevertheless,  visited  eagerly  by  bees  or  other 
insects  (e.  g.,  Grape,  Virginia  Creeper,  Mignonette 
English  Ivy,  etc.).  It  appears  quite  certain  that  it  is 
the  odor  which  attracts   them  in  these  cases.    Night- 


300  EXPERIMENTS    WITH  PLANTS 

blooming  flowers  are  proverbially  sweet-scented,  and 
doubtless  depend  principally  on  the  odor  to  attract  the 
moths  which  visit  them,  although  the  color  may  be  of 
some  assistance  also  (such  flowers  are  usually  white  or 
light  in  color).  The  question  therefore  arises,  Does  not 
color,  after  all,  play  a  subordinate  part  in  attracting  in- 
sects? especially  as  it  has  been  shown,  by  experiment, 
that  bees  and  wasps  cannot  clearly  distinguish  objects 
more  than  two  feet  away  (butterflies  and  moths  see  but 
a  few  feet) ;  while  they  can  scent  honey  for  long  dis- 
tances. In  the  case  of  flowers  which  produce  nectar 
(or  honey),  therefore,  color  would  seem  to  be  not  so 
important. 

A  very  interesting  series  of  experiments  can  readily 
be  made  by  any  one  who  has  sufficient  leisure  to  watch 
the  visits  of  the  insects  for  a  time.  Choosing  a  plant 
which  is  freely  visited,  note  the  number  of  insect  visits 
in  an  hour:  remove  the  petals  from  a  part  of  the 
flowers,  and  cover  the  remainder  with  screens  made  of 
green  leaves  (a  single  large  leaf  may  be  folded  so  as  to 
form  a  sort  of  cap  for  the  flower) .  Endeavor,  by  noting 
the  number  of  insect  visits  in  an  hour,  to  determine 
whether  the  loss  or  concealment  of  the  color  has  an 
appreciable  effect. 

The  flowers  of  many  plants  are  not  visited  by  insects 
(e.  g..  Grains  and  Grasses,  Oaks,  Hazels,  Poplars, 
etc.;  Pines  and  other  Conifers,  Palms,  Hops,  Nettles, 
etc.);  in  these  cases,  the  pollen  is  transported  by  the 


THE    WORK    OF  FLOWERS  301 

wind.  A  good  example  of  such  a  plant  is  the  Corn: 
the  anthers  (i.e.,  the  "tassel")  produce  abundant 
pollen,  which  is  carried  by  the  wind  to  the  "silk";  the 
strands  of  "silk"  are  long  stigmas,  with  projections  to 
catch  the  pollen;  the  pollen-tube  must  grow  down  the 
whole  length  of  the  "  silk."  Wind -pollinated  plants 
produce  great  quantities  of  pollen,  since  wind -pollina- 
tion is  a  very  wasteful  process.  The  pollen  from  Pine 
forests  often  forms  a  yellow  coating  on  lakes  or  on  the 
ocean  two  hundred  miles  away,  and  has  been  mistaken 
by  peasants  for  showers  of  sulphur.  The  pollen- grains 
of  the  Pine  are  provided  with  hollow  vesicles,  which 
buoy  them  up  in  the  air  very  much  on  the  principle 
of  a  box  kite:  these  may  be  easily  seen  under  the 
microscope. 

In  order  to  determine  to  what  extent  flowers  are 
dependent  on  insects  (or  wind)  for  pollination,  it  is 
only  necessary  to  enclose  them,  before  the  bud  is  open, 
in  paper  bags  (see  page  289).  If  this  be  done,  no 
fertilization  or  setting  of  seed  can  take  place  unless 
some  of  the  pollen  of  the  same  flower  arrives  on  the 
stigma.  This  is  said  to  be  self-pollination,  as  opposed 
to  cross-pollination,  which  means  bringing  the  pollen 
from  a  different  flower. 

Darwin  made  a  series  of  experiments  to  determine 
whether  cross-  or  self-pollination  is  more  advan- 
tageous. He  found  that,  in  the  case  of  the  Morning- 
glory,  cross -pollination  gave  plants  which  in  height 


302  UXPEEIMEXTS    WITH   PLANTS 

exceeded  those  from  self-pollination  as  100  to  76.  He 
carried  this  out  to  the  tenth  generation,  when  the  pro- 
portion was  100  to  54.  The  average  was  about  100  to 
77,  or  about  30  per  cent  gain.  There  was  also  a  cor- 
responding gain  in  fertility.-  In  this  case  the  cross- 
pollination  was  with  plants  growing  near  together;  on 
bringing  pollen  from  plants  growing  in  another  gar- 
den, it  was  found  that  the  plants  obtained  exceeded 
the  cross -pollinated  plants  previously  obtained  as  100 
to  78  in  height,  as  100  to  57  in  number  of  seed- pods, 
and  as  100  to  51  in  the  weight  of  seed-pods:  that  is, 
they  were  nearly  30  per  cent  more  vigorous  and,  as 
compared  with  self-pollinated,  over  44  per  cent  more 
vigorous.  Similar  results  were  obtained  with  Cabbage, 
Buckwheat,  Beets,  Corn  and  Canary  Grass. 

It  appears,  therefore,  that  cross -pollination  is  more 
advantageous  to  the  plant  than  self-pollination,  and 
there  are  numerous  devices  in  flowers  which  promote 
cross -pollination  and  prevent  self-pollination.  An 
effective  means  of  preventing  self-pollination  is  to 
have  the  anthers  and  ovaries  borne  in  separate  flowers ; 
both  kinds  of  flowers  being  on  the  same  plant,  as. 
in  the  Squash,  Walnut,  Pine,  Corn,  Castor -bean,  etc. 
(termed  monoecious),  or  the  staminate  (pollen-bearing), 
flowers  on  one  plant  and  the  pistillate  (ovary -bearing) 
on  another,  as  in  the  Hop,  Poplar,  Willow,  etc. 
(termed  dioecious).  Study  as  many  cases  of  this  kind 
as  you  can. 


THE    WOBK    OF    FLOWERS 


3Q3 


Where  both  anthers  and  seed  -  case  are  borne  in  the 
same  flower,  self-pollination  is  often  prevented  by 
having  them  active  at  different  times ;  thus  the  stigma 
is  pollinated  and  withers  long  before  the  anthers  of  the 
same  flower  are  open  in  Deutzia,  Elm  and  Plantain 
(this  method  is  especially  common  in  the  Rose,  Honey- 
suckle, Nightshade  and  Mustard  families),  while,  on 
the  other  hand,  the 
anthers  mature  first 
in  a  great  variety 
of  flowers  (espe- 
cially common  in 
Pea,  Mallow,  Pink, 
Mint  and  Composite 
families) .  This  can 
be  clearly  seen  in 
Fig.  166  (^),  which 
represents  one  of 
the  small  flowers 
from  the  center  of 
a  head  of  the  gar- 
den Gaillardia.  The 
flower  is  tubular 
and  is  represented 
as  cut  open  so  as 
to  show  the  anthers  {an) ,  which  are  united  together  to 
form  a  small  tube  into  which  the  pollen  falls  and 
so  comes  directly  on  the  stigma  {st):  nevertheless,  self- 


A 


B 


Gaillardia  flower  cut  open,  o,  bud,  showing  the 
pollen  falling  on  the  style  [st);  h,  open  flower, 
showing  the  style-branches  bent  back  ready  to  re- 
ceive pollen  from  another  flower. 


304 


HXPEBIMENTS    WITH   PLANTS 


STIC^MA 


ST/q-M/l 


pollination  does  not  take  place,  for  the  reason  that  the 
stigma  is  not  yet  mature.  In  the  process  of  develop- 
ment it  is  slowly  pushed  up,  thus  gradually  expelling 
the  pollen  from  the  tube  so  that  it  can  be  carried  away 
by  bees.  When  this  is  accomplished  it  opens  up,  as  in 
Fig.  166  (5),  exposing  the  smooth  surface,  which  is 
the  receptive  part:   the  pollen  which  is  now  deposited 

on  it  comes  from  another 
flower.  Grood  examples  of 
this  arrangement  will  be 
found  in  the  Daisy,  Aster, 
Cosmos,  Sunflower,  Core- 
opsis, Zinnia,  etc. 

Another  method  is  by 
placing  the  anthers  and 
stigma  in  different  posi- 
tions. This  is  illustrated 
by  the  Iris  (Fig.  167).    As 

167.    Iris  flower,  showing  how  the  stigma  thC    bCC    CUtCrS     the     flOWCr 
first  removes  the  pollen  from  the  bee,  . 

after  which  the  anther  deposits  a  fresh  thc      S  1 1  fif  m  a      SCrapCS      Off 
supply,  which  is    carried    to    another  *-'  ■•• 

^^'^^'"-  some   .of   the   pollen  with 

which  its  back  is  covered:  as  it  goes  deeper  into  the 
flower  its  back  receives  a  fresh  supply  from  the  an- 
ther: as  it  backs  out  of  the  flower  this  pollen  is  not 
deposited  on  the  stigma  (owing  to  the  manner  of  its 
attachment  to  the  style),  but  is  carried  on  to  the  next 
flower. 

The  behavior  of  the   Partridge -berry  (also  called 


THE    WORK    OF  FLOWERS 


305 


Fig. 
one  of  these  the  anthers  are 


A/l^ 


-AN 


ST 


168, 


Twinberry,  Checkerberry,  Deer  berry  and  Squaw -vine) 
illustrates  another  method.  Fig.  168  represents  two 
flowers  cut  open.  In 
placed  high  up  in  the 
tube,  while  the  stig- 
mas are  below:  in  the 
other  the  reverse  is 
true.  The  bee,  in 
thrusting  its  long 
tongue  into  A^  receives 
the  pollen  on  the  lower 
portion  of  the  tongue 
and,  going  to  5,  de- 
posits it  on  the  stig- 
mas: in  going  from  B 
to  ^,  it  would  receive  the  pollen  on  the  upper  portion 
of  its  tongue  and  deposit  it  on  the  stigmas  in  the  corre- 
sponding position.  On  going  from  A  to  another  flower 
of  the  same  kind,  the  pollen  from  A  would  not  reach 
the  stigma,  and,  even  if  it  should,  experiments  indicate 
that  it  would  not  take  effect:  it  is  eflective  only  when 
deposited  on  a  stigma  of  corresponding  position.  A 
similar  arrangement  is  found  in  the  cultivated  Prim- 
rose and  in  the  Houstonia  (also  called  Quaker  Ladies 
and  Quaker  Bonnets). 

The  Sage  has  a  neat  device  for  the  purpose  of  load- 
ing the  bee  with  pollen  and  preventing  self-pollination. 
Fig.  169    (^)   represents    the   flower- tube   cut  open, 


,  Partridge -berry  flower  cut  open:  the  bee's 
tongue  receives  pollen  upon  its  lower  portion  in 
a,  from  the  anthers  {an),  and  deposits  it  on  the 
corresponding  stigma  {si)  in  6,  and  vice  versa. 


306 


EXPERIMEXTS    WITH  PLANTS 


showing  the  anther  {an)  with  a  bee  entering  and  about 
to  strike  his  head  against  the  lower  part  of  the  anther- 

stalk.  The  stalk  of  the 
anther  turns  on  a  hinge 
or  pivot,  so  that,  when 
the  lower  part  is  struck, 
down  flops  the  anther 
and  discharges  pollen 
all  over  the  bee  (Fig. 
169,  B) .  In  the  mean- 
time the  stigma  {st)  is 
up  out  of  the  way,  but 
when  the  pollen  is  all 
discharged  it  grows 
down  and  takes  the  po- 
sition shown  in  Fig.  169, 
C.  When  a  bee  en- 
ters such  a  flower  the 
pollen  is  transferred  di- 
rectly to  the  stigma. 
There  are  numerous 
other  devices  for  loading  the  insect  with  pollen,  in- 
cluding the  pumping  mechanism  of  the  Pea  flower,  the 
irritable  stamens  of  Barberry,  Prickly  Pear,  etc., 
which  spring  when  touched  at  the  base,  thereby  scat- 
tering pollen  on  the  insect,  and  also  the  curious 
arrangements  found  in  Orchids.  An  account  of  these, 
together  with  other  matters  concerning  pollination,  will 


,  Sage  flowers  cut  open:  a,  a  bee  entering 
the  flower;  ft,  an  anther  {an)  striking  the 
bee;  c,  the  stigma  {st)  of  an  older  flower 
removing  pollen  from  the  bee. 


THE    WORK    OF   FLOWERS  307 

be  found  in  Kerner  and  Oliver's  "  Natural  History  of 
Plants,"  Vol.11.  See  also  Miiller,  "Fertilization  of 
Flowers";  Weed,  "Ten  New  England  Blossoms";  New- 
ell, "Outlines  of  Lessons  in  Botany";  Gibson,  "Sharp 
Eyes"  and  other  books;  Lubbock,  "British  Wild  Flow- 
ers"; Darwin,  "The  Various  Contrivances  by  which 
Orchids  are  Fertilized  by  Insects." 

The  peculiar  shapes  of  flowers  are  usually  adapta- 
tions to  the  visits  of  insects,  either  for  the  purpose  of 
securing  cross -pollination  or  covering  the  insects  with 
pollen,  or  affording  platforms  on  which  they  may  alight, 
such  as  the  lower  lip  of  the  Sage  (Fig.  169) .  See  also 
Iris  (Fig.  167)  and  examine  the  Pea,  etc.  It  is  an  in- 
teresting experiment  to  watch  how  the  bee  alights  on 
the  flower;  and,  when  this  is  ascertained,  carefully  cut 
away  the  platform  or  other  support,  and  notice  the 
subsequent  behavior  of  the  bees. 

In  such  flowers  as  the  Pea  and  Sage,  it  is  quite  evi- 
dent that  the  position  of  the  flower  is  of  importance.  If 
it  should  accidentally  be  turned  upside  down  and  w^ere 
unable  to  right  itself,  the  platform  would  be  out  of 
place  and  the  devices  for  loading  the  insect  with  pollen 
would  not  operate;  the  same  is  true  of  a  great  many 
other  flowers.  Moreover,  we  notice  that  in  many  cases 
the  old  and  the  young  flowers  assume  different  posi- 
tions, as  in  the  Clover,  Poppy,  Strawberry,  Labur- 
num, Geranium,  Honeysuckle,  etc. ;  the  general  effect 
of  this  is  to  get  the  young  flowers  which  are  not  yet 


308  EXPERIMENTS    WITH  PLANTS 

ready  for  pollination,  and  the  old  flowers  which  have 
been  pollinated,  out  of  the  way  of  the  insects  which 
visit  the  flowers.  What  determines  the  position  of  the 
flower  and  fruit?  If  the  plants  are  growing  in  pots,^ 
invert  thern;  place  some  in  the  dark  and  others  in 
the  light,  and  observe  the  effect  on  the  flowers.  If  the 
flowers  are  in  a  long  cluster,  keep  the  main  stalk 
from  bending  by  attaching  a  small  weight  to  the  end, 
and  then  observe  the  behavior  of  the  individual  flowers. 
Try  the  effect  of  placing  the  plant  in  a  horizontal 
position.  What  parts  bend!  Do  the  flowers  resume 
their  original  position  ?  Is  the  result  due  to  light,  or 
gravity,  or  to  both?  Are  the  movements  performed 
by  the  stalks  alone  if  the  flowers  are  removed  ? 

In  the  Snapdragon,  Pea,  etc.,  notice  that  when  the 
bee  alights  on  the  lower  lip,  the  flower,  which,  up  to 
that  time  is  closed,  opens  as  the  result  of  its  weight. 
A  smaller  insect  would  not  be  able  to  get  into  the 
flower,  since  its  weight  would  not  suffice  to  bend  the 
lower  lip.  This  is  an  advantage,  since  it  keeps  out 
small  insects,  and  especially  creeping  insects,  which 
would  not  distribute  the  pollen  advantageously.  An- 
other device  for  keeping  out  creeping  insects  is  a 
band  of  woolly  or  sticky  hairs  below  the  flower,  which 
serves  the  same  purpose  as  the  tar  applied  to  the 
trunks    of   trees.     In   other   cases   a  mass  of   woolly 

ilf  the  plants  are  not  in  pots,  the  flowering  branches  may  be  carefully 
bent  downward  or  cut  oflf  and  placed  in  water,  and  then  inverted. 


THE    WOBK   OF   FLOWERS  309 

hairs  in  the  tube  of  the  flower  constitutes  an  effective 
defence. 

In  many  plants  (especially  among  Pears,  Plums 
and  Grapes)  pollen  from  the  same  flower  or  even  from 
another  individual  of  the  same  species  is  without 
effect :  pollen  from  another  variety  must  be  employed 
in  order  to  set  the  fruit.  This  is  usually  accomplished 
by  planting  a  few  trees  of  the  proper  variety  in  the 
orchard,  so  that  the  bees  may  carry  the  pollen.  This 
condition  is  known  as  self- sterility,  and  is  frequently 
brought  about  by  hybridization  or  even  by  cultivation. 
Climate  may  also  assist  in  bringing  it  about ;  it  is 
noticed  that  some  varieties  which  are  self- sterile  in 
the  North  are  not  so  in  the  South. 

The  effect  of  pollination  and  fertilization  is  not 
confined  to  the  seed,  but  extends  to  the  seed -case 
and  often  to  surrounding  parts.  Thus,  the  pulpy  part 
of  the  Strawberry  consists  of  the  swollen  end  of  the 
stalk,  which  is  stimulated  to  grow  as  the  result  of  the 
fertilization  of  the  seeds.  In  the  Apple  the  fleshy  part 
is  partly  the  wall  of  the  ovary  and  partly  the  calyx  : 
the  fruit  has  five  compartments,  and,  if  the  seeds  in 
only  one  or  two  of  these  are  fertilized,  the  fleshy  growth 
around  these  compartments  is  stimulated  more  than 
elsewhere,  producing  a  one-sided  fruit.  Just  how  the 
development  of  the  seed  influences  that  of  surrounding 
parts  is  not  known,  but  it  seems  to  be  due  to  chemical 
changes  which  take  place  in  the  developing  embryo. 


310  .EXPElUMEyXS    WITH   PLAXIS 

In  the  Fig  the  end  of  the  stalk  develops  as  a 
hollow,  fleshy  structure,  which  is  lined  with  numerous 
flowers  closely  crowded  together  (like  the  flowers  in  a 
Sunflower  head).  These  produce  the  seeds ^  which  we 
see  in  the  Fig  as  it  comes  on  the  market.  In  some 
varieties  the  Fig  develops  without  fertilization,  while 
in  others  it  drops  off  without  developing  unless  the 
seeds  are  fertilized.  This  peculiarity  of  Figs  has  led 
to  a  great  amount  of  confusion  which  has  only  recently 
been  cleared  up.- 

Aristotle  described  the  practice  known  as  caprifica- 
tion  as  it  is  still  practiced  today.  It  consists  of  taking 
figs  from  the  Wild  Fig  (or  "caprifig")  and  hanging 
them  in  the  branches  of  the  cultivated  Fig  tree  of  the 
orchards.  Ever  since  the  time  of  Aristotle,  scientifi(; 
men  have  disputed  whether  this  process  were  useful 
or  not.  Recently  it  has  been  shown  that  in  the  case 
of  the  best  Figs  of  commerce,  i.e.,  the  Smyrna  Figs, 
the  process  is  absolutely  necessary,  while  in  the  case 
of  some  others  it  is  not.  The  key  to  the  puzzle  lies  in 
the  fact  that  the  most  valuable  varieties  of  Figs  are 
like  the  Hop  plant  in  having  the  pollen- bearing  flowers 
on  one  plant  and  the  seed- bearing  flowers  on  another. 
The  "wild  Fig,"  or  "caprifig,"  is  the  pollen -bearing 
plant,  and  when  its  figs  are  hung  in  the  branches  of 

1  Each  one  of  these  "seeds"  is  really  a  fruit,  since  it  is  contained  in  a 
separate  seed-case. 

2  See  the  article  by  Swingle  on  "Smyrna  Fig  Culture  in  the  United  States," 
in  the  Year-Book  of  the  Department  of  Agriculture  for  1900. 


TEE    WORK   OF  FLOWERS  311 

the  orchard  Fig  (which  is  the  seed- bearing  plant)  tiny 
wasps,  all  covered  with  pollen,  creep  out  of  the  capri- 
figs  and  enter  the  edible  figs,  and  so  pollinate  the  flow- 
ers, which  consequently  are  enabled  to  set  seed.  It  is  the 
seed  which  gives  to  the  Smyrna  Figs  the  peculiar  nutty 
flavor  which  makes  them  so  valuable  for  the  market. 

The  Smyrna  Figs  do  not  develop  fruit  without  fer- 
tilization: they  contain  true  seeds.  The  Mission  Fig 
of  California  and  other  varieties  which  develop  fruit 
without  fertilization  have  no  true  seeds,  but  only  hollow 
shells  containing  no  embryos. 

For  a  long  time  there  has  been  a  belief  that  the  pol- 
len can  not  only  stimulate  the  growth  of  the  seed- case 
and  surrounding  parts  but  also  influence  their  color, 
form,  etc.  (this  phenomenon  is  known  as  Xenia).  A 
white  Corn  pollinated  with  a  dark  Corn  produces  in 
'the  course  of  the  same  summer  an  ear  with  white  and 
dark  kernels  mingled,  giving  the  ear  a  very  curious 
appearance.  Examination  shows  that  in  this  case  it 
is  not  the  seed -case  whose  color  is  affected  but  the 
seed  itself;  it  is  the  endosperm  of  the  seed  which  is 
colored,  and  this  arises  from  a  nucleus  which,  like  the 
Qg^  nucleus,  fuses  with  a  nucleus  from  the  pollen -tube 
(Fig.  164),  and  so  can  receive  the  qualities  of  the  pol- 
linate parent.  Many  different  kinds  of  evidence  go  to 
show  that  the  nucleus  is  the  bearer  of  hereditary 
qualities,  and  that  where  two  nuclei  fuse  the  resulting 
nucleus  bears  the  qualities  of  both, 


CHAPTER   VII 

THE    WORK    OF    FRUITS 

The  first  work  of  the  fruit  ^  is  to  convey  nourish- 
ment to  the  young  seeds  (ovules)  and  protect  them 
during  their  development.  How  great  is  the  impor- 
tance of  the  food  supply  to  the  seeds  is  shown  by  the 
fact  that  there  is  never  enough  to  develop  all  of  them, 
so  that  a  fierce  struggle  ensues  among  them  to  deter- 
mine which  shall  develop  at  the  expense  of  the 
others.  You  can  see  evidences  of  this  struggle  in 
almost  any  young  fruit  you  open.  Almost  from  the 
first,  certain  seeds  take  the  lead  and  grow  larger  than 
the  others,  and  these  are  usually  the  ones  which  in  the 
end  absorb  all  the  nourishment  from  the  others  so  that 
the  latter  shrivel  up  and  finally  disappear.  The  strug- 
gle among  the  individual  fruits  on  the  plant  is  just  as 
vigorous;  many  must  perish  in  order  that  a  few  may 
mature.  It  is  often  necessary  to  thin  out  the  fruit  in 
an  orchard  several  times  in  a  season,  so  that  the 
ground  under  the  trees  is  each  time  covered  with  fruit. ^ 

^  The  word  fruit  as  here  used  means  any  ripe  (or  ripening)  ovary  or  seed- 
case,  with  its  contents  and  any  other  parts  pertaining  to  it. 

2  In  thinning,  the  grower  proceeds  on  the  assumption  that  the  amount  of 
fruit  (by  weight)  is  much  the  same,  whether  thinning  is  practiced  or  not;  but 
by  thinning  he  gets  this  in  the  form  of  fewer  and  larger  fruits.  Thinning 
must  be  done  with  good  judgment. 

(312) 


THE    WORK    OF  FRUITS  313 

It  is  clear  that  to  mature  the  seeds  properly  there 
must  be  a  good  food  supply  and  some  means  of  con- 
veying it  directly  to  the  developing  seeds  as  fast  as 
needed.  We  have  already  noticed  that  a  large  amount 
of  food  is  stored  up  in  preparation  for  flowering.  This 
is  especially  noticeable  in  such  plants  as  the  Carrot, 
Turnip,  Parsnip,  etc.  Find  out,  by  means  of  the  tests 
mentioned  on  pages  164-166,  the  kind  of  food  stored 
in  these  roots.  Make  the  tests  also  on  any  bulbs  which 
are  available  (especially  Onion,  Hyacinth,  Lily,  etc.): 
in  these  the  food  is  stored  in  the  leaves.  Examine 
also  some  underground  stems  which  are  used  for  stor- 
age (such  as  the  rhizome  of  Iris,  Solomon's  Seal,  tuber 
of  Potato,  etc.),  and  make  tests  to  see  what  kinds  of 
food  they  contain.  How  does  the  stored  food  reach  the 
seeds?  Endeavor  to  trace  the  starch  from  the  rhizome, 
bulb  or  other  storehouse  up  into  the  seeds.  The 
other  foods  may  be  traced  also,  though  not  quite  so 
easily  as  the  starch.  In  what  tissues  of  the  stem  and 
fruit  do  they  travel?  Examine  several  trees  which 
have  starchy  seeds,  such  as  the  Oak,  Buckeye,  etc. 
Where  is  the  starch  stored;  in  what  tissue  does  it 
travel  to  the  seed? 

How  completely  the  stored  food  may  be  used  up  is 
seen  in  the  case  of  Grains.  During  the  season  of 
growth  the  plant  is  engaged  in  storing  up  starch  and 
other  foods,  with  the  result  that  the  stalks  are  very 
nutritious  and  eagerly  eaten  by  animals.    When   the 


314  EXPERIMENTS    WITH  PLANTS 

seed  begins  to  ripen  the  plant  stops  growing  and 
the  stored  food  moves  toward  the  seeds,  where  it 
becomes  concentrated,  leaving  the  stalks  empty  of 
nutriment  so  that  they  cannot  be  used  as  food  for  cat- 
tle. The  withdrawal  of  food  from  the  stalk  goes  on 
after  the  stalk  is  cut,  consequently  the  best  time  for 
cutting  grain  is  just  before  it  is  fully  ripe ;  it  can  then 
be  transported  without  loss  of  seeds  by  shaking,  and 
will  absorb  nutriment  from  the  stalk  and  ripen  as  well 
as  if  left  uncut  (this  does  not  apply  when  the  grain  is 
"headed,"  i.  e.,  when  the  head  is  removed  from  the 
stalk  by  a  special  machine  known  as  a  "header").  For 
a  forage  crop,  like  hay,  cut  after  the  seeds  are  formed 
but  before  they  are  ripe. 

A  great  number  of  plants  (annuals,  biennials,  also 
the  Century  Plant,  etc.)  resemble  the  Grains  in  giving 
up  all  their  store  of  food  to  the  seeds,  and  dying  after 
the  seed  is  ripe.  Is  the  food  transformed  on  reaching  the 
fruit?  The  seeds  of  the  Rape  contain,  while  develop- 
ing, much  starch,  which  can  be  traced  from  the  leaves 
directly  to  them;  but,  when  mature,  this  is  all  changed 
into  proteids  and  fats.  Examine  any  available  plants 
which  have  oily  seeds  or  fruits,  to  see  if  the  same  is 
true  of  them. 

In  fruits  and  seeds  which  contain  large  quantities  of 
sugar,  is  there  any  indication  that  starch  accumulates 
and  is  subsequently  transformed  into  sugar  ? 

Along  with  the  production  of  sugar  there  is,  in  many 


THt]    WOl^K    OF   riWlTS  ;^15 

fruits  (e.  g.,  Currant,  Raspberry,  etc.),  a  marked  pro- 
duction of  acid.  It  is  these  fruits  which  are  principally 
used  in  the  preparation  of  jams,  jellies,  etc.  The 
"  jelling "  depends  on  the  presence  of  gelatinous  sub- 
stances (pectin  compounds  and  allied  substances)  which 
are  present  in  the  ripe  fruit  and  are  increased  in 
quantity  by  boiling  the  fruit;  in  this  process,  the  acid 
contained  in  the  fruit  acts  on  various  substances  and 
transforms  them  into  other  substances  which  readily 
"  jell";  in  the  young  fruit,  these  bodies,  as  well  as  the 
acids,  are  lacking  to  such  an  extent  that  such  fruits 
can  not  be  used  for  jelly- making.  On  the  other  hand, 
they  disappear  from  over -ripe  fruit  to  such  an  extent 
that  it,  too,  is  unfit  for  this  purpose. 

Along  with  these  changes  which  occur  during  the 
process  of  ripening,  go  changes  in  the  sugar -content. 
The  young  fruit  is  either  tasteless  and  insipid  or  else 
acrid  and  sour;  as  it  approaches  ripeness,  it  gets 
sweeter,  and  the  sugar  may  accumulate  to  such  an  ex- 
tent as  to  almost  completely  mask  the  taste  of  the  acid 
(which  is,  however,  still  present  in  undiminished 
amount).  The  sweetness  (and  the  characteristic  flavor) 
of  the  fruit  is  increased  by  dryness  and  warmth: 
mountain -grown  fruit  is,  for  this  reason,  sweeter;  over- 
irrigated  fruit  is  insipid.  Sweetness  may  also  be  in- 
creased in  some  cases  by  appropriate  fertilizers,  and, 
even,  in  the  case  of  oranges,  by  spraying  the  fruit  with 
chemicals. 


316  EXPERIMENTS    WITH   PLANTS 

The  color  of  the  fruit  also  undergoes  changes  in 
ripening;  in  this,  light  plays  a  great  part.  Try  the 
experiment  of  covering  a  green  apple  (which  is  well 
exposed  to  light)  with  tin- foil  (held  in  place  by  elastic 
bands),  in  which  a  circle  or  letter  has  been  cut  (in 
France  there  is  a  practice  of  attaching  photographs  to 
the  fruit  in  this  manner) . 

The  changes  which  occur  in  the  ripening  fruit, 
whereby  some  substances  disappear  and  others  take 
their  places  (or  result  from  their  transformation),  go 
on  after  the  fruit  is  detached  from  the  plant,  as  is 
evident  from  the  familiar  practice  of  placing  pears  in 
drawers  to  ripen.  In  order  to  control  these  processes 
and  preserve  the  fruit  properly,  special  methods  have 
been  developed.  Thus  it  is  found  that  pears  which 
ripen  fully  on  the  tree  are  much  more  gritty  than  those 
gathered  earlier  and  placed  (not  more  than  three  or 
four  deep)  in  trays,  and  kept  in  a  cool,  rather  dry 
room,  with  little  circulation  of  air.  It  is  very  important, 
in  picking  all  kinds  of  stalked  fruits,  to  leave  the  stalk 
attached  to  them,  since  its  removal  leaves  a  wound, 
which  readily  softens  and  decays.  It  is  important  to 
keep  the  fruit  in  a  cool  place,  and  to  avoid  exposing  it 
to  the  sun;  otherwise  the  ripening  and  subsequent 
decay  will  proceed  rapidly.  The  ideal  method  is  to  put 
the  fruit  in  cold  storage. 

Water,  as  well  as  food,  is  needed  by  fruits.  Many 
fruits  when  ripe  contain  from  90  to  96  per  cent  water.. 


THE    WORK    OF  FRUITS  317 

How  does  this  reach  them?  A  squash  or  a  pumpkin 
is  a  favorable  object  for  study  :  it  may  take  up  as 
much  as  a  pound  and  a  half  of  water  in  twenty -four 
hours.  Cut  a  young  growing  squash  from  the  vine 
and  place  the  cut  end  in  eosin  solution,  and  allow  it 
to  stand  for  several  days.  Trace  the  eosin  up  through 
the  bundles  to  the  seeds.  Do  you  find  a  bundle  reach- 
ing to  each  seed  ?  Does  the  bundle  grow  larger  as  the 
seed  develops?  Does  the  fruit  lose  water  by  transpi- 
ration? Test  this  matter  in  the  fashion  already 
described  for  leaves.  Do  you  find  any  stomata  in  the 
epidermis  of  the  fruit  (examine  microscopically  and 
also  test  in  the  air-pump).  Grapes  are  of  especial 
interest  in  this  connection  :  examine  also  apples, 
pears,  etc.  Admirable  means  of  protection  against 
transpiration  are  found  in  the  thick,  woody  walls  of 
nuts,  drupes  (Peach,  Eucalyptus,  etc.). 

Does  the  fruit  need  a  supply  of  air?  Repeat  the 
experiment  shown  in  Fig.  31,  using  immature  fruits 
instead  of  seeds.  Try  the  effect  of  smearing  over 
young  fruits  completely  with  vaseline  :  does  it  retard 
their  development?  Do  they  contain  much  air  in 
their  tissues  ?  Place  some  of  the  tissue  (preferably  a 
piece  of  watermelon  flesh)  under  water  in  the  air- 
pump,  and  exhaust. 

How  does  the  air  travel  through  the  stalk,  etc.,  to 
the  fruit?  Investigate  by  the  methods  previously 
described. 


318  JSXPEBIMEXTS    WITH   PLANTS 

In  order  to  increase  the  production  of  fruit,  various 
methods  are  employed.  The  best  method  is  to  increase 
the  vigor  of  the  tree  by  good  tilth  and  occasional 
application  of  fertilizers.  In  applying  fertilizers,  it  is 
to  be  noted  that  nitrogen  tends  to  produce  vegetative 
growth  at  the  expense  of  fruit,  while  phosphoric  acid 
tends  rather  to  produce  fruit  (this  effect  of  phosphoric 
acid  has  been  demonstrated  in  some  cases  but  not 
generally)  :  potash  is  probably  the  most  necessary 
fertilizer  for  orchards. 

If  the  growth  is  so  vigorous  that  the  tree  produces 
wood  at  the  expense  of  fruit,  this  tendency  may 
be  checked  by  seeding  down  for  a  time,  decreasing 
the  amount  of  tillage  and  using  mineral  rather  than 
nitrogenous  fertilizers. 

A  local  check  is  often  applied,  in  the  case  of  a 
branch  which  does  not  bear,  by  ringing  or  girdling. 
This  varies  in  degree  from  simply  running  a  knife 
around  the  branch  near  its  base  to  removing  a  strip 
of  bark  from  one  to  several  inches  wide  (see  p.  257), 
or  simply   by  cutting  a  notch. 

Partially  cutting  off  the  water  supply  by  bending, 
twisting,  breaking  or  notching  the  branch  often  causes 
it  to  bear.  In  bending  the  branch,  it  is  turned  down- 
ward and  fastened  in  that  position.  This  method  is 
used  most  frequently  for  Grapes  and  fruit  trees  trained 
against  walls.  Twisting  acts  like  bending  but  more 
energetically  ;   the  branch  is  twisted  half-way  round  ; 


THJ-J    WOIfK    OF   FRUITS  319 

splits  are  made,  which  consequently  become  filled  with 
parenchyma,  and  a  swelling  forms  at  the  twisted  place. 
The  branch  is  subsequently  bent  to  form  a  loop. 
In  layering  Quinces,  branches  are  twisted  whenever 
roots  are  to  be  formed.  In  some  localities  the  stems 
of  nearly  ripe  grapes  are  twisted,  thus  diminishing 
the  water  supply  and  making  the  grapes  sweeter. 
Breaking  the  branch  over  the  blade  of  a  knife  acts 
like  twisting.  Pruning  the  roots  or  simply  laying  them 
partially  bare  is  sometimes  resorted  to  with  excellent 
results.  In  this  connection  it  is  interesting  to  note 
that  a  drought  (or  a  frost)  often  starts  the  trees  of 
an  entire  region  to  fruiting  at  the  same  time.  It  has 
been  observed  that  the  attacks  of  borers,  by  checking 
the  growth,  often  cause  trees  to  bear :  for  the  same 
reason,  driving  nails  into  Plum  and  Peach  trees  some- 
times causes  them  to  bear. 

It  is,  of  course,  well  known  that  the  exposure  of 
the  land  has  much  to  do  with  fruitfulness.  For  this 
reason  vineyards  are  placed  on  hillsides  with  a 
southern  exposure,  and  vines  and  fruit  trees  are  fre- 
quently trained  against  walls  with  like  exposure.  Pro- 
tection from  wind  is  also  important,  since  the  wind 
dries  young  fruits  and  causes  them  to  fall  and  also 
lowers  the  temperature  :  for  this  reason  windbreaks 
are  indispensable  in  many  orchards. 

To  summarize,  then,  we  may  say  that  in  order  to 
produce  abundant  fruit  we  must  provide  for  an  early 


320  EXPHJRIAflJNTS    WITH   PLANTS 

and  generous  development  of  foliage  ;  as  the  fruiting 
season  approaches,  decrease  of  water  and  increase  of 
light  and  heat  are  desirable:  succulent  fruits  require 
more  water  than  others. 

Protection  of  the  seeds  from  animals  and  insects 
is  accomplished  in  various  ways.  Look  out  for 
exam]3les  of  the  following : 

{a)  Spines,  etc.  (Chestnut,  Thorn-apple  or  Jim- 
son -weed). 

(h)  Hard  coverings*  (Pines,  Eucalyptus,  nuts, 
Peach,  etc.). 

(c)  Bitter  or  acrid  taste  while  young,  disappearing 
with  ripeness  (orchard  fruits,  berries,  etc.). 

(d)  Suspension  on  slender  stalks  protects  from 
mice,  etc.  (Pea). 

(e)  Concealment  under  ground  (Peanut,  some 
Evening   Primroses) . 

The  outer  covering  of  a  fruit  also  acts  as  a  pro- 
tection against  parasitic  fungi  and  against  too  rapid 
drying. 

When  the  fruit  is  ripe  its  work  is  not  yet  done, 
for  the  seeds  must  be  scattered  as  much  as  possible 
in  order  that  they  may  propagate  far  and  wide  :  this 
dissemination  is,  in  most  cases,  the  work  of  the  fruit. 

Gather  a  quantity  of  nearly  ripe  pods  of  the  Lu- 
pine, and  place  them  on  the  floor  of  an  unused  room 
where  they  may  dry  properly.  As  they  become  dr}^, 
peculiar  cracking  sounds  are  heard  and  the  seeds  are 


THE    WORK    OF   FRUITS 


321 


thrown  to  a  distance  of  several  feet.  Try  to  discover 
by  what  mechanism  this  is  accomplished  ;  notice  the 
twisting  of  the  pod  which  accompanies  the  expulsion 
of  the  seeds  ;  how  is  this  twisting  brought  about? 
Many  other  members  of  the  Pea  family  have  this 
peculiarity.  Interesting  to  study  in  this  connection  n 
are  the  fruits  of  the  Touch-me-not,  Violet,  q  q 
Wood-sorrel  (Oxalis),  Witch-hazel  and  many  q 
others.  The  Squirting  Cucumber  (Fig.  170) 
throws  its  seeds  twenty  feet  or  more  by 
means  of  a  curious  contrivance. 
The  end  of  the  stalk  is  enlarged  to 
form  a  sort  of  stopper.  The  fruit 
is  filled  with  a  mucilaginous  sub- 
stance in  which  the  seeds  are  im- 
bedded. When  this  has  absorbed 
considerable  water,  sufficient  pres- 
sure is  generated  so  that  a  touch 
causes  the  stopper  to  be  ejected j 
and  the  seeds  are  sent  flying. 

While  these  wonderful  contrivances  serve  excel- 
lently to  distribute  the  seeds  for  a  short  distance, 
they  are  but  poor  and  ineffective  compared  to  those 
which  make  use  of  the  wind  as  a  carrier.  Thistle- 
down flies  to  great  distances  ;  the  fruits  of  Maples, 
Elms,  Pines,  Birches,  etc.,  travel  far  and  wide  by 
the  aid  of  the  wind.  On  windy  days,  when  the  snow 
is  covered  with  a  smooth  crust,  such  fruits  go  skim- 


no.  Fruit  of  Squirting  Cu- 
cumber in  the  act  of  ex- 
pelling the  seeds:  the 
fruit  absorbs  water  un- 
til sufficient  pressure  is 
generated  to  eject  the  en- 
larged stopper- like  end 
of  the  stalk  and  the  seeds 
with  it. 


u 


322 


EXPERIMENTS    WITH  PLANTS 


ming  over  its  surface  at  a  high  rate  of  speed,  and 
every  footprint  is  soon  carpeted  with  them.  On  the 
plains  the  Russian  Thistle  and  other  "  tumble- 
weeds"  are  blown  over  the  level  surface  of 
the  ground,  scattering  their  seeds  at  every 
step  (in  this  case  the  whole  plant  assists  in 
the  dissemination). 

The  problem  of  flying  is  solved  in  various 
ways:  sometimes  the  calyx  is  modified  into  a 
parachute  (Dandelion,  Thistle,  etc.) ;  some- 
times the  style  (Clematis,  Fig.  171)  is  used 
for  this  purpose;  a  bract  may  serve  as  a 
wing  (Linden,  Fig.  172,  and  Hop,  Fig.  173), 
or  the  wall  of  the  ovary  may  grow  out  into  a 
flattened  wing  -  like  appendage 
(Maple,  Fig.  174),  w^hile  in  other 
cases  it  is  the  seed- coat  which 
grows  out  in  this 
(Pines) .  Find  out  what  you  ( 
about  this.  A  very  simple 
way  of  testing  the  effec- 
tiveness of  these  flying  de- 
vices is  to  drop  the  seeds 
from  a  height  down  a  stair 
well  or  wherever  the  air  is 
still,  and  time  them  in 
their  fall  to  the  earth. 

Are  the  flying  attach- ^'^-  "trJ^f^.taV":''''™'" 


^ 


171.  Clem- 
atis fruit, 
which  flies 
by  means 
of  the 
feathery 
style. 


THE    WORK    OF   FRUITS 


323 


ments  of  seeds,  especially  the  parachutes,  impaired  by 

rain  and  dew  f    Test  them  by  placing  them  in  water ; 

are  they  readily  wetted  f    You  have  probably  noticed 

that  fruiting  Dandelion  heads  open 

only  in    dry,    sunny   weather,   when 

the  seeds  can  fly  to  best  advantage; 

at  the  approach  of   rain   they   close 

up  tight,  so  that  the  tiny  parachutes 

are  kept  perfectly  dry.     Study  also 

the  Willow  Herb  (Epilobium)  and  the 

Pines  in  this   connection.     In   many   173.  Hop  fruit,  which  mr 

cases   you  will    find  that  while   the      by  means  of  a  bract. 

seeds  are  not  protected  froc! 
rain,  and  may  become  drenched 
yet  they  do  not  become  de- 
tached from  the  parent  plant 
until  perfectly  dried  out  and  in 
condition  for  flying. 

The    burs,    "  stickers,"   and 

^^  wli^wL^h'gtws^'LTr^^^^       either  troublesome  fruits  which 

wall  of  the  seed-case  (ovary).  ^^.^^^j^     thcmSelveS     tO    clotMug, 

show  how  easily  plants  distribute  them- 
selves by  means  of  animals.  Usu- 
ally the  organs  of  attachment  are  not 
borne  on  the  seed  itself,  but  on  the 
ovary -wall,  on  bracts  or  on  the  stem 
or  flower- stalk.  On  examining  such 
fruits  (Figs.  ]75  to  178)  with  a  hand-       175.  Burdock  head. 


324 


EXPERIMENTS    WITH  PLANTS 


lens,  we  see  that  they  are  covered  with  spines,  prickles, 
hooks,  claws  or  barbs  of  the  most  various  description, 
so  that  we  may  say  that  plants  have  tried 
almost  every  possible  device  in  solving 
this  particular  problem.  Many  fruits  are 
sticky,  and  will  cling  even  to  the  smooth- 
est  surfaces,  while  some,  like 

176.    Fruit  of  Bur  '  ,         i  •    i 

Clover.  the  Tar  weeds,  are  both  sticky 

and   armed  with  hooks,  so  that  they  cling 
equally  well  to  rough  and  smooth  objects. 

A  simple  way  to  test  the  efficiency  of  these 
devices  is  to  toss  them  against  a  blanket 
hanging  vertically,  and  notice  which  cling 
most  readily  to  its  surface.  Examine  the 
coats  of  animals  to  see  what  plants  are  most 
successful  in  attaching  their  seeds  or  fruit!-. 
Many  seeds  are  carried  about  by  birds 
(and  other  animals)  in  the  mud  which  sticks 
to  them.  This  is  especially  the 
case  with  such  birds  as  frequent  Beggars-ticks. 
swampy  and  muddy  places.  Birds  distribute 
seeds  principally,  however,  by  eating  the 
berries  and  other  fleshy  fruits,  and  after- 
wards voiding  the  seeds  uninjured.  Such 
fruits  are  usually  sour,  acrid  or  otherwise 
disagreeable  to  the  taste  during  their  development ;  but, 
when  ripe,  become  sweet  and  fine-flavored:  at  the  same 
time  they  assume  a  characteristic  and  usually  conspic- 


177.     Fruit  of 


178.    Fruit  of 
Clotbur. 


THE    WORK   OF  FBUITS  325 

nous  coloration,  whereby  the  fact  of  then*  ripeness 
is  advertised  to  the  birds  which  feed  upon  them.  The 
bright  tints  and  sweet  taste  of  the  fruits  thus  serve  a 
similar  purpose  to  the  honey  and  gay  colors  of  the 
flowers.  Experiments  have  been  made  to  test  the  ger- 
minating power  of  seeds  which  have  passed  through 
the  digestive  tract  of  birds,  with  the  result  that  the 
seeds  germinated  readily.  Cherry,  Apple  and  Juniper 
trees  are  frequently  planted  by  birds  in  this  way, 
especially  along  roadside  fences,  etc.,  which  are 
frequented  by  them. 

What  seeds,  especially  of  plants  growing  by  brooks, 
streams  and  lakes,  are  able  to  float?  Place  such  seeds 
in  water,  and  see  how  long  it  takes  them  to  sink. 
Examine  any  accessible  water- course  for  evidences  of 
distribution  of  seeds  by  water. 

The  Cocoanut  (Fig.  45)  seems  especially  designed 
for  floating,  inasmuch  as  its  outer  fibrous  husk  forms 
a  veritable  life-preserver;  it  has  been  known  to  float 
hundreds  of  miles  on  the  surface  of  the  ocean.  On 
reaching  a  strand,  it  readily  germinates;  in  this  way 
coral  and  volcanic  islands  in  the  South  Seas  are 
populated  with  Cocoanut  Palms. ^ 

1  On  seed  distribution  see  Kerner  and  Oliver;  Natural  History  of  Plants, 
Vol.  II;   Beal:   Seed  Dispersal, 


CHAPTER   VIII 

HOW    PLANTS    ARE    INFLUENCED    BY    THEIR 
SURROUNDINGS 

We  have  already  learned  that  the  needs  of  the  plant 
correspond  closely  to  our  own  physical  needs:  they 
consist,  namely,  of  food,  water,  light,  air  and  warmth. 
Depriving  a  plant  of  any  one  of  these  kills  it:  on  the 
other  hand,  an  excess  of  any  of  these  is  usually  as  bad 
as  an  insufficiency.  In  situations  where  all  these  needs 
are  properly  supplied,  plants  grow^  to  perfection;  but 
such  situations  are  limited  in  extent,  and,  in  the  fierce 
competition  to  which  plants  are  subject,  many  are 
forced  to  grow  in  unfavorable  situations  or  not  at  all. 
How  they  make  the  best  of  these  situations  and  adapt 
themselves  to  them  is  an  interesting  study,  w^hich  is 
best  approached  by  experimental  methods\ 

Water. — Let  us  begin  with  the  influence  of  water  on 
the  plant.  An  excellent  plant  to  illustrate  this  is  the 
Potato.  A  potato  contains  sufficient  water  to  sprout 
by  itself,  even  when  kept  rather  dry:  if  a  potato  wiiich 
has  just  started  to  sprout  is  placed  where  it  is  not 
exposed  to  direct  sunlight,  it  will   continue  to  grow 

1  See  an  article  by  Webber  in  the  Year  Book  of  the  U.  S.  Dept.  of  Agricul- 
ture for  1895. 

(326) 


BO^V    PLANTS    A  ME    INFLUENCED 


327 


lying  on  a  dry  table -top,  and  will  finally  assume  the 
appearance  1  shown  in  Fig.  179.  On  comparing  it 
with  a  potato 
grown  under 
normal  con- 
ditions, we 
see  that  its 
growth  has 
been  exceed- 
ingly slow 
(the  normal 
Potato  of  the 
same  age  is 
a  hundred  or 
more  times 
as  large),  its 
branches  are 
thick  and 
clumsy  in 
appearance, 
with  close- 
ly crowded 
nodes  ;2      it 


179.  Potato  which  has  been  allowed  to  sprout  and  grow  on  a  dry 
table-top  before  a  north  window,  showing  Cactus-like  habit. 


1  A  somewhat  similar  but  less  pronounced  effect  is  produced  by  the  action 
of  strong  light,  even  when  abundant  moisture  is  present:  in  general,  the  effects 
of  light  and  dryness  are  closely  similar.  Fig.  180  shows  the  striking  contrast 
between  potato  sprouts  which  receive  little  water  and  abundant  light,  as  com- 
pared with  those  which  receive  abundant  water  but  no  light.  In  the  latter  the 
nodes  are  further  apart  and  the  stem  more  elongated  and  much  weaker  than  in 
a  normal  plant,  while  the  leaves  are  small  and  the  whole  plant  of  a  pale  color. 

2  The  nodes  are  the  places  where  leaves  and  buds  appear  on  the  stem. 


328 


EXPERIMENTS    WITH    PLANTS 


bears  no  leaves,  but  their  work  is  performed  by  the 
green  rind  of  the  stem  and  branches.  As  compared 
with  the  normal  plant,  the  loss  of  water  in  per  cent  of 

its  own  weight  is 
ver}^  small.  Just 
how  much  it 
amounts  to  we  may 
determine  by  weigh- 
ing at  intervals , 
For  purposes  o  f 
comparison  we  may 
cut  off  a  branch  of 
the  normal  Potato, 
trim  off  the  lower 
end  until  the  branch 
weighs  about  the 
samo  as  the  other, 
and  then  place  it 
with  the  cut  end  in 
water,  over  which 
we  pour  a  little  cotton-seed  or  olive-oil.  We  now  deter- 
mine loss  of  weight  in  the  usual  way  and  compare  (tests 
should  be  made  under  the  same  conditions  for  both) . 

If  we  take  sections  of  the  stem  we  find  that,  as 
compared  with  a  normal  plant,  the  cuticle  is  thicker, 
the  cells  are  much  smaller,  and  are  very  densely  filled 
with  starch,  i.  e.,  the  stem  is  used  as  a  place  for  stor- 
age of  food. 


180.  The  potato  at  the  left  grew  iu  u  moist  place  in 
dai'kness:  the  one  at  the  right  grew  in  a  dry  place 
iu  strong  light:  both  grew  for  the  same  length  of 
time. 


sow    PLANTS    ABE    INFLUENCED 


329 


All  these  features  are  very  characteristic  of  desert 
plants ;  in  fact,  the  whole  appearance  and  behavior  of 
this  plant  reminds  one  of  a  Cactus. 

On  the  other  hand,  we  may,  by  growing  a  Cactus 
in  the  dark,  with  abundant  moisture,  cause  the  spines 
to  grow  out  into  succulent,  leaf- like  organs.  Fig.  181 
shows  a  sprout  which 
has  grown  from  a 
Prickly  Pear  under 
these  conditions.  It 
will  be  noticed  that  the 
sprout  appears  cylin- 
drical, and  that  in  its 
whole  appearance  it  is 
more  like  an  ordinar}^ 
plant  than  is  the  Potato 
plant  shown  in  Fig. 
179.  This  sprout  was 
obtained  by  taking  a 
joint  of  Prickly  Pear 
which  was  preparing  to 
sprout,  placing  it  in  a 
pot  of  sand,  and  set- 
ting this  inside  a  closed 
box  to  exclude  the  light. 
It  was  watered  frequently,  and  in  the  course  of  about 
two  months  produced  the  sprout  shown  in  the  figure. 

We   believe   that  the  ancestors  of  the  Cactus   had 


■ 

^M^  ^9 

^M 

^^^^1 

^^^  ^  f^l 

^^HT  .981 

■ 

^H^\ ..  I^^H 

mm 

1 

1^ 

m       *'    j^^gfi^^B 

^1 

r  i'"i| 

1 

^^^^^^^  '^^1 

i^  1 

l>-\.-' 

■•^^^v  m 

■1 

181.    Sprout  of  Prickly  Pear  grown  iu  the  dark, 
showing  leaf-like  organs. 


330  EXPERIMENTS    WITH  PLANTS 

leaves  like  ordinary  plants  and  that  their  thickened, 
leafless  stems  have  been  brought  about  by  the  dry 
conditions  under  which  they  have  lived,  not  directly 
as  in  the  Potato,  but  by  a  long- continued  process  of 
change.  We  suppose  that  when  the  ancestors  of  the 
Cactus  first  came  to  live  under  drier  conditions  than 
they  were  accustomed  to,  some  few  of  them  were  some- 
what better  adapted  to  stand  drought  and  so  lived  on 
and  propagated  themselves  under  the  new  conditions, 
while  their  fellows  perished.  Among  the  offspring  of 
these  plants  the  same  thing  happened  ;  those  best  fitted 
to  the  new  conditions  maintained  themselves,  while 
the  others  perished.  In  each  succeeding  generation  the 
fittest^  survived  and  crowded  out  the  less  fit  in  the 
struggle  for  existence,  the  result  being  that  in  the 
course  of  time  the  plant  became  better  and  better  fitted 
to  its  surroundings.  In  this  way  we  suppose  the  vari- 
ous forms  of  Cacti  to  have  developed  to  their  present 
condition,  this  process  of  development  being  known 
as  evolution.  It  will  be  seen  from  the  illustration  that 
evolution  works  by  destroying  the  unfit ^  (thus  giving 
the  fit  a  better  chance  to  develop),  and  results  in 
bringing  the  plant  into  better  and  better  harmony 
with  its  surroundings,  or  environment.  The  process  of 
destroying  the  unfit  and  preserving  the  fit  is  called 

1  Whether  the  fittest  originated  gradually  or  suddenly  (by  mutation)  is  dis- 
cussed in  Chapter  X. 

2  This,  it  should  be  said,  is  not  the  sole  method  by  which  evolution  works, 
but  the  only  one  of  immediate  importance  in  this  connection. 


S01V   PLANTS    AliU    INFLUENCED 


331 


"natural  selection,"  and  finds  a  close  parallel  in  artifi- 
cial selection  as  practiced  by  man  in  adapting  plants 
to  his  needs.  All  our  farm  and  garden  plants  have 
been  brought  to  their  present  condition  largely  by 
artificial  selection.^ 

We  believe  that  all  the  various  kinds  of  plants 
and  animals  have  reached  their  present  condition  by 
evolution  and  that  evolution  is  still  going  on,  though 
at  a  compara- 
tively  slow  rate. 

An  examina- 
tion of  plants 
which  live  in  dry 
situations  shows 
that  they  have  the 
following  charac- 
teristics.- 

(1)  Reduced 
surface,  obtained 
by  suppression  of 
leaves  (complete 
or  nearly  so) .  This  is  accompanied  by  thickening  of 
stems  in  the  Cacti  (Fig.  182),  some  of  which  assume 
a  spherical  form,  which  gives  a  minimum  surface.  The 
Switch  Plants,  such  as  the  Gorse  (Fig.  198,  a),  Cytisus 
(Fig.  183),  etc.,  assume  the  form  of  green,  rod-like 
switches. 

1  See  Chapter  X. 

2  For  experiments  on  this  subject,  see  pages  215-218. 


182.  A  spherical  Cactus;  a  form  which  presents  the 
minimum  surface  for  evaporation  with  a  maximum 
liulk  for  storage. 


332 


EXPERIMENTS    WITH   PLANTS 


The  discarding  of  leaves   in  winter  by  deciduous 
trees  and  shrubs  is  an  adaptation  to  the  drought  from 
which  the  plant  suffers  in  winter,  since  the  roots  are 
then   unable    to    absorb    sufficient 
water  to   supply  the  leaves.    We 
may    test    this    by    the    following 
experiment  :    Take    two    vigorous 
plants  growing  in  pots ;  place  one 
on  ice  (by  means  of  the  arrange- 
ment shown  in  Fig.  11) ;  keep  the 
other  near  it   at  normal  tempera- 
ture;  give  both  the  usual  quantity 
of  water.    Which  plant  wilts  first? 
On     continuing     the     experiment 
for  a  few  days,  it  will   be  found 
tl^^:1ZJ:Z^Z   that   the    plant    on   ice    sheds   its 
perform  the  work  of  leaves.    |g^^^g    (Begouia    may    bc    rccoui- 

mended  for  this  experiment). 

The  fall  of  the  leaf  is  preceded  by  the  withdrawal 
of  all  nutriment  from  it  and  the  formation  of  a  layer 
of  loose  cells  at  the  base  of  the  stalk  ;  this  layer 
finally  breaks  apart,  leaving  a  clear,  smooth  scar 
(see  page  212).  The  disorganization  of  the  chloro- 
phyll gives  rise  to  the  gorgeous  colors  of  autumnal 
foliage  and,  while  not  caused  by  frost,  is  hastened 
by  it. 

Trees  which  retain  their  leaves  in  winter  have 
various  devices  to  restrict  evaporation.    Study  in  this 


183.  Branch  of  Cytisus  (a  switch 


EOW  PLANTS    ABE    INFLUENCED  333 

respect  Pines,  Spruces,  Holly,  etc.  The  branches  are 
protected  against  evaporation  by  cork  and  bark  ;  the 
buds,  by  gums,  varnishes,  wax,  hairs,  etc.  (see  page 
214). 

(2)  Reduced   surface  obtained   by  having  smaller 
leaves  (Moor  plants,  Heaths,  etc). 

(3)  Eeduced  air  content  obtained  by  diminishing 


184.     Steins  of  Callitriche  in  cross-section:  (a)  land  form,  (6)  water  form. 
Showing  the  larger  air  spaces  in  the  latter. 

the  size  of   the  interior  air-spaces  (Callitriche,   Fig. 
184). 

(4)  Reduced  evaporation  obtained  by  means  of 
thickened  epidermis,  as  seen  in  Cacti,  Century  Plant, 
Holly  (Fig.  185),  Oleander  (Fig.  192),  and  most 
plants  of  dry  situations. 

(5)  Reduced  evaporation  obtained  by  means  of 
coverings  of  wax  (Sugar-cane,  Fig.  186,  Eucalyptus, 
Iris,  Spruce),  or  hairs  (Dusty  Miller,  Wormwood  or 


334 


DXPEBIMENTS    WITH  PLANTS 


185.    Epidermis  of  Holly,  with  thick 
cuticle  (c). 


8age   Brush   [Fig.   1871,    Mullein    [Fig.   188],   Jdive- 
finger,  Immortelle,  coverings  of  many  winter -buds),  or 

varnish  and  resin   (cover- 

N^  ings  of  most  winter- buds 

and     many    leaves    when 

young;     Cistus,    Pines. 

0000^(    etc.). 

(6)  Reduced  evapora- 
tion obtained  by  rolling 
the  leaves  (Corn,i  many 
Grasses)  or  keeping  them 
in  a  vertical  position  (Eu- 
calyptus, Iris). 

(7)  Storage  of  water 
(and  food)  in  thickened 
leaves  (Live-for-ever,  Cen- 
tury Plant,  Hen-and- chick- 
ens) ,  or  in  thickened  stems 

186.    Waxy  covering  of  Sugar  Cane  (in  the     (Cactl,      Fig.       18*j,       Ctc). 

The  stored  food  and  water 
are  tempting  to  many 
animals,  hence  the 
Cacti  are  protected 
by  sharp  spines.  The 
Century  Plant  is  pro- 
tected by  the  sharp 
points  of   its  leaves: 


form  of  rod-like  outgrowths). 


187.    Hairs  of  Wormwood  or  Sage-brush. 


iSee  page  213. 


HOW    PLANTS    ABE    INFLUENCED 


335 


it  goes  on  storing  up  food  for  several  years,  when  it 
blooms  and  uses  up  the  nutriment  stored  in  the  leaves, 
then  dies. 
Hence  the 
name,  Century 
Plant,  due  to 
the  popular 
belief  that  it 
blooms  but 
once  in  a  cen- 
tury. 

(8)  More 
abundant 
woody  fiber 
(see  Pigs.  189' 
and  190) . 

(9)  Longer  palisade  cells  in  the  leaf  (Fig.  194). 

(10)  Reduction   in  number  of   stomata  (Fig.  191) 
and  sinking  of  the  stomata  in  wells  and  depressions 

(Oleander,    Fig.    192). 

All  plants 
growing  in  dry 
situations  show 
some  of  these 
characteristics, 
and  many  of 
them  can  be 
produced  in 


188.     Hairs  of  Mullein. 


190.  Cross-section  of  stem  of 
Water-polygonum  grown  in 
water;  the  fibrous  bundles 
and  strengthening  tissue 
are  shaded. 


189.  Cross-section  of  stem  of 
Water-polygonum  grown  in 
dry  soil;  the  fibrous  bundles 
and  strengthening  tissue  are 
shaded. 


336 


EXPERIMENTS    WITH   PLANTS 


any  plant  by  growing  it  with  a  reduced  amount  of 
moisture.  Make  such  experiments  as  you  can  on  this 
point. 

Study  every  case  you  can^  and,  if  possible,  make 
experiments,  by  growing  the  plants  in  pots  (or  plots) 
and  regulating  the  amount  of  water  given  them. 


191.  Upper  epidermis  of  Water-polygonum :  UO  from  m  leaf  of  a  plant  cultiviited  under 
dry  conditions,  (.b)  from  the  first  leaf  produced  by  such  a  plant  after  being  placed 
in  water,  showing  a  larger  number  of  stomata. 

It  may  seem  surprising  to  find  that  many  plants 
which  grow  in  damp  places  show  the  features  de- 
scribed above  :  such  are  plants  growing  in  alkali  soils, 
or  along  the  seashore  where  the  water  is  brackish.  The 
explanation  is  that  in  these  places  there  are  substances 
in  the  water  which  hinder  its  absorption  by  the  roots 
(see  page  124). 

1  Plants  subject  to  the  drying  action  of  strong  winds  show  these  features 
excellently. 


HOW    PLANTS    A  BIS    INFLUENCED 


337 


192.  Cross-section  of  a  leaf  of  Ole- 
ander, showing  the  stomata  (s) 
sunken  in  depressions,  which  are 
filled  with  hairs. 


Very  different  in  appearance 
are  the  plants  which  inhabit 
streams  and  lakes,  such  as  the 
Water-lily,  Sjjatterdock,  Ar- 
rowhead, etc.,  which  are  typical 
water-plants,  with  broad  thin 
leaves,  devoid  of  hairy  cover- 
ings and  provided  with  enor- 
mous air-spaces,  especially  in 
the  leaf -stalk.  These  great  air- 
spaces are  necessary  to  convey 
air  down  to  the  roots  and  other 
submerged  parts  of  the  plant. 
The  submerged 
leaves    (and 


submerged  parts)  of  water- 
plants  obtain  air  from  the 
water  (see  pages  193  and  283 
for  experiments) ;  the  leaves  i/v 
are  usually  split  up  into  fine 
divisions  by  which  a  greater 
surface  is  secured.  Fig.  193 
shows  the  behavior  of  the 
Arrowhead,  which  produces 
ribbon-like  leaves  under  water 

and  the    characteristic    Arrow-     193.   Arrowhead,  producing  rlbbon-liUe 

leaves  below  the  surface  {w)  of  the 

head  leaves  above  water.  The       S'TuS'eTSeTJirt'.'lhrr^dYel? 

figure      also      shows       a       heart-  {Mtorr^s^a  transition  between  the 


338 


EXPEBIMENTS    WITH   PL  A  XT  S 


shaped  leaf,  a  transition  form  between  the  two.  Fig. 
194  shows  at  (?))  a  section  of  a  submerged  portion  of 
a  ribbon-like  leaf,  while  at  {a)  is  a  section  of  a  por- 


194.  Cross-section  of  the  ribbon-shaped  leaves  of  Arrowhead,  (a)  from  a  part  of 
a  leaf  above  the  water,  (6)  from  a  part  of  a  leaf  below  the  surface,  showing 
thinness,  lack  of  cuticle  and  larger  air-spaces. 

tion  of  a  ribbon-like  leaf  which  projected  into  the  air. 
Fig.  195  {a)  shows  a  submerged  leaf  (water  -  leaf)  of 
the  Water  Buttercup,  while  beside  it  {!))  is  another 
leaf  which  grew  above  the  water  (air- leaf) .  The  Water 
Buttercup  presents  a  transition  from  a  land -plant  to  a 
water-plant.  If  the  water  sinks,  so  that  the  sub- 
merged leaves  are  exposed  to  the  air,  they  dry  up  and 
perish,  while  the  air -leaves  live  on  and  the  plant 
continues  to  flourish. 

We  have  good  reason  to  believe  that  the  water- 
plants  (with   the  exception  of  certain  groups  of  flow- 


MOW    PLANTS    AME    INFLUENCED 


339 


erless  plants)  were  originally  land -plants  which 
were  forced  by  competition  to  take  to  the  streams 
and  lakes.  Some  of  them  still  possess  the  power 
to  live  on  land  if  the  water  falls  away,  while  others 
can  live  only  in  water  and  quickly  perish  when  left 
without  it  (Hornwort,  Water-lily,  Pondweed,  etc.). 
The  water-plants  in  general  show  exactly  opposite 
features  to  those  already  enumerated  as  characteristic 
of  desert -plants.  They  have  a  large  exposed  surface, 
thin  cuticle,  no  waxes,  varnishes,  resins  or  hairs  on 
the  surface,  a  minimum  amount  of  woody  fiber,  very 
large     air-spaces     and     poorly     developed     palisade. 


195.    Leaves  of  the  Water-buttercup:   (a)  water-leaf,  (6)  air-leaf. 

Stomata  occur,  as  a  rule,  only  on  surfaces  which  are 
directly  exposed  to  air  (Fig.  196). 

Water-plants  have  usually  a  very  poorly  developed 
root- system  :  many  of  them  have  no  roots  at  all,  but 
float  about  on  the  water,  sinking  to  the  ])ottom  on  the 


340  JiJXPElilMENTS    WITH  PLANTS 

approach  of  cold  weather  and  rising  to  the  surface 
again  in  the  spring.  Such  plants,  as  a  rule,  have  the 
custom  of  breaking  up  into  pieces,  each  of  which  floats 
away  and  becomes  a  separate  plant. 

A  very  interesting  experiment  may  be  made  by 
growing  the  Water- hyacinth  in  soil  instead  of  in  water 
and  observing  the  modifications  it  undergoes.  We  may 
also  use  the  Water- polygonum  for  this  experiment. 


196.  Lower  epidermis  of  Water-polygonum;  (a)  from  a  submerged 
leaf,  showing  lack  of  stomata,  {b)  from  an  air-leaf  produced  by 
a  plant  growing  in  water. 

Water  affects  the  size  of  every  part  of  the  plant 
noticeably,  as  may  be  seen  by  comparing  plants  grown 
in  dry,  sandy  soil  with  the  same  species  grown  with 
abundant  water  (e.  g.,  the  weeds  which  come  up  in  a 
garden  as  compared  with  those  which  grow  in  dry 
spots). 

The  large  wood -cells  produced  in  the  spring  (spring 
wood),  as  contrasted  with  the  fall  wood,  are  another 
illustration  of  this  (see  page  247).    A  scion  grafted  07i 


ROW   PLANTS   ABJ!]   INFLUENCED  341 

a  stock  which  supplies  it  overabundantly  with  water 
forms  a  mass  of  large -celled  wood- parenchyma  in  place 
of  ordinary  wood. 

It  is  often  very  noticeable  that  the  leaves  which  are 
formed  during  a  dry  period  are  small  and  stunted, 
while  those  subsequently  formed  on  the  same  branch 
during  a  rainy  period  may  be  four  or  five  times  as 
large. 

The  roots  of  many  plants  branch  in  a  peculiar, 
compact  fashion  when  they  grow  in  water  (for  example, 
the  roots  of  trees  when  they  enter  a  cistern  or  drain- 
pipe), hence  the  popular  name,  "  water-roots." 

Very  interesting  results  are  obtained  when  we  grow 
ordinar}^  land -plants  in  a  saturated  atmosphere,  in  the 
manner  shown  in  Fig.  157.  Select  a  bulb  (or  corm, 
tuber,  etc.)  which  has  begun  to  sprout:  cut  out  a  piece 
(two  or  three  inches  long)  bearing  a  sprout  at  one  end, 
place  it  in  a  dish,  and  cover  it  with  a  lamp-chimLey. 
Pour  in  some  water,  and  cork  the  chimney,  covering 
the  cork  with  sealing-wax  or  vaseline.  The  air  within 
the  chimney  will  soon  become  saturated  with  moisture, 
and  its  influence  on  the  growth  of  the  plant  can  be 
readily  observed.  The  tissue  at  the  base,  which  is  in 
contact  with  the  water,  will  eventually  decay;  but  this 
will  not  interfere  with  the  growth  of  the  sprout.  The 
results  of  growing  Dandelion  leaves  and  Gorse  in  this 
way  are  shown  in  Figs.  197  and  198. 

Water  seems  to  have  a  direct  influence  on  the  pro- 


34'J 


iJXPJi'Ji'IMENTS     WITH    PLANTS 


duction  of  flowers  and  fruit.    Land- plants  growing  in 
unusually  moist  situations  run  to  stem  and  leaf,  and 
produce    flowers    and    fruit    sparingly:    on   the 
contrary,  when  growing  in  unusually  dry  places, 
the  same  plants  produce  relatively  more  abun- 
dant flowers  and  fruit  than  usual .    Such  water- 
plants   as  are  descended  from  land -plants  are, 
as  a  rule,  unable  to  flower  or  fruit  under  water 
(Water   Plantain,  Arrowhead,   Hippuris,  etc.). 
Gardeners   induce   plants   to  flower  abundantly 
by  digging  a  trench   around    the    base   of  the    \\\) 
trunk,  and  thereby  cutting  off  numerous  active 
roots:    another    method    is    to    simply    lay    the 
roots  bare.    Cacti  which  are  allowed  to  become 
somewhat  dry  and  shrunken  bear  more  freely. 

Bending  and  breaking  the  branches  of  fruit 
trees,  which  results  in  partially  cutting  off  the 
water    supply,    is    practiced    for    the    purpose 
of    causing   trees    to    fruit.     It    also    tends    to 
make    the    fruit    sweeter    and    of    higher 
flavor.     Fruit    grown    in    the    mountains 
(where  it  is  dryer  and  the  light  stronger) 
is  usually  superior  in  these  respects.  Over- 
irrigation     has    a    tendency     to    produce 
watery  fruit  which  is  neither  very  sweet 

nor    highly    flavored. ^  197.   Leaves  of  Dan- 

-pv       1  •  •        J        1  T    1  T  delion   drawn   on 

-By  knowing  lust  when  and  how  much  to     the  same  scale:  («) 

normal,  (&)  grown 
I  See  pages  318  and  319.  SoyheT'^'  '"*'" 


HOW    PLANTS    AMU    INFLUENCED 


343 


irrigate,  we  may  hope  to  control  very  largely  both  the 
quantity  and  quality  of  the  crop.  At  present  there  is 
so  much  confusion  in  this  regard  that  we  may  find  one 
farmer  using  several  times  as  much  water  as  his  neigh- 
bor for  the  same  kind  of  crop  grown  under  the  same 


198.    Gorse:  (a)  leafy  form,  the  result  of  growing  in  a  saturated  atmosphere, 
(6)  normal  (leafless)  form,  the  branches  transformed  to  spines. 

gene^-al  conditions.  In  general,  crops  cannot  be  grown 
to  advantage  when  the  soil  contains  more  than  50  to 
60  per  cent  of  the  total  amount  it  is  capable  of  hold- 
ing. The  study  of  irrigation  is  bound  to  be  of 
increasing  importance,  since  it  is  becoming  evident 
that  it  will  pay  to  irrigate,  even  in  regions  where  the 
rainfall  is  now  ordinarily  regarded  as  amply  sufficient 
for  crops  (see  pages  130  and  131). 


344 


EXPERIMENTS    WITH    PLANTS 


Light. — The  effect  of  light  on  the  plant  is  ordinarily 
much  the  same  as  that  of  dryness.  In  fact,  some  of 
the  effects  of  strong  light  are  due  to  the  increased  trans- 
piration which  it  produces.  In  the  case  of  the  desert- 
plants,  etc.,  the  effects  of  the  two  are  difficult  to 
distinguish.  There  are,  however,  many  effects  of  light 
which   are   independent   and    are   manifested   equally 


199.     Leaves  of  Prickly  Lettuce  seen  in  cross-section:   (a)  sun  leaf,  (6)  shade  leaf. 

well   when   the   plant  is  grown  in  a  saturated  atmos- 
phere. 

Some  plants  (sun -plants)  prefer  the  direct  sun- 
shine, while  others  grow  only  in  the  shade  (shade- 
plants).  The  latter  (e.  g.,  many  Ferns,  etc.)  have 
leaves  of  paler  color,  relatively  large  and  thin,  and 
not  well  adapted  to  withstand  direct  sunlight :  if 
exposed  to  it  they  soon  die.  Similar  differences  may 
be  found  in  leaves  growing  on  the  same  plant  when, 


HOW    PLANTS    ABU    INFLifENGED 


345 


as  often  happens,  some  of  them  are  directly  exposed 
to  the  sun  while  others  are  continuously  shaded.  Figs. 
128  and  130  show  two  branches  from  the  same  plant : 
the  one  shown  in  Fig.  128  was  well  illuminated,  while 
the  one  shown  in 
Fig.  130  was  shaded: 
there  is .  a  corre- 
sponding difference 
in  the  size  of  the 
leaves.  Fig.  199 
shows  the  appear- 
ance of  sections  of 
sun-  and  shade - 
leaves  of  the  Prickly 
Lettuce  and  Fig. 
200  of  sun-  and  shade -leaves  of  the  Beech.  Especially 
noticeable  in  the  "sun-leaf''  are  the  longer  palisade 
cells,  the  smaller  air-spaces,  the  greater  thickness  of 
the  leaf,  and  thicker  cuticle  or  outer  wall  of  the 
epidermal  cells  ;  the  number  of  stomata  is  also 
smaller.  These  effects  are  due  partly  to  the  liglit 
itself  and  partly  to  the  dryness  (or  excessive  evapo- 
ration) caused  by  the  light,  heat  and  wind. 

Leaves  arrange  themselves  with  reference  to  the 
direction  of  the  light,  and  many  follow  the  sun  during 
the  day  (see  page  217).  Some  plants,  inhabitants  of 
dry  countries,  place  their  leaves  in  a  vertical  position, 
thus   avoiding  the   full    effect  of   the   light    (see  page 


200.    Beech  leaves  seen  in  cross-section: 
(a)  sun  leaf,  (&)  shade  leaf. 


346  EXPElilMENTS    WITH  PLANTS 

217).  The  leaves  of  the  compass  plants  are  vertical 
and  directed  north  and  south.  Many  leaves  tempora- 
rily assume  a  vertical  position  in  very  strong  sunlight 
(see  page  217),  and  it  is  noticeable  that  young  leaves, 
which  are  more  sensitive  to  the  light  than  the  older 
ones,  usually  assume  this  position.  (Plants  can  be 
grown  by  electric  light ;  and  this  has  proved  profitable 
in  forcing  certain  greenhouse  crops  in  winter.) 

The  trunks  of  trees  may  suffer  from  "sunscald,"  due 
to  injury  of  the  bark  by  the  intense  light  and  heat  of 
the  sun,  or  to  the  alternate  thawing  and  freezing  of  the 
bark  on  the  southwest  side  in  late  winter.  The  trouble 
may  be  obviated  by  shading  the  trunk  with  a  screen  of 
wire,  boards,  cornstalks,  etc.  Pruning  often  lets  in  too 
much  light  on  the  trunk,  which  suffers  in  consequence 
(this  is  especially  noticeable  in  the  Weeping  Willow) . 

Very  interesting  results  are  obtained  by  growing- 
plants  in  darkness.  To  do  this  out-of-doors,  it  is  only 
necessary  to  cover  the  plant  with  a  section  of  stove- 
pipe, a  wooden  box  or  a  barrel.  Within  doors  the 
plant  may  be  placed  in  a  dark  closet  or  box.  Such 
plants  (Figs.  103  and  180)  have  very  long,  slender 
stems  (the  nodes  are  far  apart)  ;  they  are  pale  in 
color,  have    little  woody  fiber, ^  and    are  consequently 

1  This  fact  is  taken  advantage  of  in  bleaching  Asparagus,  Celery  and 
Rhubarb  for  market.  The  Celery  is  either  "hilled  up  "  or  covered  with  gunny- 
sacks,  or  the  light  is  excluded  by  means  of  boards  :  the  leaf-stalks  are  thus 
bleached  and  rendered  tender  and  succulent.  The  "laying,"  or  lodging  of 
Wheat  is  due  to  the  shading  of  the  lower  portion  of  the  stalk,  which  results  in 
an  insufficient  production  of  woody  fiber. 


now    PLANTS    ABE    INFLU hJNCJiW  347 

weak.  The  leaves^  (hi  most  plants)  remain  small  and 
pale  in  color.  Hairs  and  even  prickles  tend  to  dis- 
appear in  darkness. 

It  is  well  known  that  intense  light  causes  a  greater 
intensity  of  coloring  of  fruits,  flowers  and  other  colored 
parts  of  plants:  this  is  especially  noticeable  in  moun- 
tain regions.  Compare  the  colors  of  flowers  in  shady 
woods  with  those  in  the  sunlight  of  open  meadows. 

Light  also  affects  the  abundance  of  flowers  and 
fruit.  Many  plants  bloom  little  or  not  at  all  in  poor 
light,  while  in  strong  light  they  do  so  abundantly. 
This  is  noticeable  in  house -plants  cultivated  at  a  north 
or  northeast  window,  as  compared  with  those  grown  at 
a  south  window.  The  effect  is  due  partly  to  the  fact 
that  with  better  light  the  leaves  produce  more  food  for 
the  nourishment  of  the  flowers  and  fruit,  partly  to  the 
direct  action  of  the  light  (and  temperature)  on  the 
organs  themselves.  If  possible,  make  experiments  on 
this  point.  Some  plants  can  be  kept  for  years  in 
healthy  vegetative  condition  at  an  intensity  of  illumi- 
nation which  is  too  low  to  permit  them  to  blossom. 
Observe  plants  that  are  partially  shaded  (as  by  a  house 
or  hedge) ,  and  note  especially  whether  more  blossoms 
are  formed  (blossoms  formed  on  one  side  may,  by 
twisting,  appear  on  the  other)  on  the  side  which  is 
shaded  or  on  the  side  which  is  exposed  to  the  light. 

1  In  many  Monocotyledons  the  leaves  continue  to  grow  in  darkness.  The 
scale-leaves  of  subterranean  stems  often  develop  into  green  forage-leaves  if 
exposed  to  light  (e.  g.,  Hawkweeds). 


348 


EXPERIMENTS    WITH   PLANTS 


In  making  these  observations,  it  will  probably  be 
noticed  that  many  flowers  grow  toward  the  light  and 
place  themselves  so  as  to  receive  it  as  directly  as  pos- 
sible. This  has  a  useful  purpose  in  making  them  much 
more  conspicuous  to  insects.    See  page  298. 

Wind. —  Every  one  is  more  or  less  familiar  with  the 


201.     The  effect  of  wind  on  the  growth  of  a  tree  trunk. 

effects  of  wind  on  plants.  Near  the  seacoast,  or  on 
mountains,  or  wherever  trees  are  exposed  daily  to 
strong  wind,  they  show  by  their  bent  forms  and  curi- 
ous shapes  its  potent  influence  (Fig.  201).  The  dying 
of  the  branches  on  the  windward  side  (Fig.  202)  is 
due  to  the  drying  effect  of  the  wind,  which  may  in- 
crease transpiration  as  much  as  twentyfold  (see  page 
208).  Even  moist  winds  may  have  a  drying  effect. 
It  is  interesting  to  observe  how  the  one-sided  develop- 
ment of  leaves  and  branches  affects  the  stem.    This  is 


HOW    PLANTS    ABE    INFLUENCED 


349 


well  shown  in  Fig.  203.    It  may  be  observed  in  vines, 
etc.,  which  climb  on  walls. 

The  effect  of  wind  in  drying  up  the  blossoms  of 
fruit  trees,  etc.,  is 
well  known.  For  this 
reason,  and  also  be- 
cause the  winds 
lower  the  tempera- 
ture and  do  consid- 
erable damage  to 
trees  laden  with  ice 
and  snow,  the  use  of 
windbreaks  is  often 
indispensable. 

Food.— We  have 
already  learned 
(pages  137  to  162) 
that  the  kind  of  min- 
eral food  th^  plant  1 
receives  affects  its 
growth  and  general 
appearance .  Thus, 
abundance   of    nitrogen  ^  causes  a  particularly  strong, 

1  See  articles  by  Riley  and  by  Woods  in  the  Year  Book  of  the  U.  S.  Depart- 
ment of  Agriculture  for  1901. 

2 It  is  an  interesting  fact  that  abundant  manuring  with  nitrogen,  combined 
with  abundant  watering,  very  commonly  produces  "green  flowers,"  i.  e.,  flowers 
in  which  petals,  stamens  and  even  ovules  are  transformed  into  green  leaf  -  like 
bodies.  This  happens  frequently  in  garden  Asters  and  other  Compositae.  In 
some  cases  this  greening  of  the  flowers  is  caused  by  the  attacks  of  plant-lice 


202.    The  effect  of  wind;  branches  stuiited 
and  killed  on  the  windward  side. 


350 


EXPERIMENTS    WITH    PLANTS 


203.     How  one-sided  development  of  branches  affects  the 
trunk.     (See  Fig.  202). 


rank  vegetative  growth  and  imparts  a  deep  green  to 
the  leaves,  while  phosphorus  especially  promotes  the 
production  of  flowers  and  fruit.    It  is  a  well-known  fact 

that  starving 
a  plant  makes 
it  flower  and 
fruit  m  u  c  h 
earlier.  De- 
priving it  of 
water  has  the 
same  effect 
(seepage  318). 
An  excess 
of  a  particular 
substance  in  the  soil  may  render  it  unfit  for  some 
plants,  while  others  flourish  in  it.  Thus,  Asparagus 
svill  stand  so  much  salt  that  the  weeds  in  an  Aspara- 
gus bed  may  be  killed  by  sprinkling  on  salt,  while  the 
Asparagus  itself  is  not  injured. 

Soil  too  alkalnie  for  ordinary  crops  will  raise  Sugar 
Beets  and  Alfalfa,  while  land  too  alkaline  for  these 
crops  will  grow  Salt  Bush,  which  makes  good  fodder. 

Peat  Moss  or  Sphagnum  is  killed  by  a  small 
amount  of  lime,  while  other  Mosses  flourish  on  lime- 
stone rocks  and  in  water  containing  large  quantities 
of  dissolved  lime.  The  presence  or  absence  of  lime 
usually  has  a  marked  effect  on  the  flora.  Some  plants 
are  known  as  lime  loving,  others  as  the  reverse. 


IIO]V    PLANTS    ABE    INFLUENCED  351 

Some  plants  are  found  only  in  sour  humus  (either 
in  wet  humus,  as  Peat  Mosses,  Sundew,  etc.,  or  in  dry 
humus,  as  Heath  plants),  while  others  are  found  only  in 
"mild"  humus  (Dog's  Mercury,  Cow  Wheat,  etc.): 
some,  indeed,  are  found  only  in  a  particular  kind  of 
humus,  e.  g.,  that  of  Conifers  (Rattlesnake  Plantain). 
Observe  all  you  can  in  regard  to  the  occurrence  of 
plants  in  different  kinds  of  soils.  To  a  certain  extent 
each  kind  of  soil  is  characterized  by  certain  plants. 
This  has  been  noticed  by  prospectors,  who  have  found 
that  certain  plants  are  found  only  where  certain  metals 
(e.  g.,  zinc)  abound. 

A  fuller  understanding  of  the  kind  of  soil  preferred 
by  different  plants  ^  will  not  only  enable  us  to  better 
suit  our  crops  to  our  land,  but  be  of  great  assistance  in 
determining  the  availability  of  hitherto  uncultivated 
land  for  various  crops. 

Not  only  the  chemical,  but  more  especially  the 
physical  character  of  the  soil  and  of  the  subsoil 
(whether  hard-pan  or  porous),  is  of  importance  in  this 
connection.  Find  out  what  kind  of  land  is  considered 
most  suitable  for  the  various  crops  with  which  you  are 
familiar.  Try  also  to  cultivate  the  ability  to  judge  of 
the  character  of  the  land  by  the  wild  plants  which  grow 
on  it.  Such  plants  are  indicators  not  only  of  the 
chemical  and  physical  character  of  the  soil,  but  also  of 
the  temperature  and  other  important  factors  of  climate. 

1  The  United  States  Department  of  Agriculture  is  now  making  soil  surveys 
in  various  states,  to  determine  what  crops  are  best  adapted  to  various  soils. 


352  EXPERIMENTS    WITH  PLANTS 

Heat. — At  the  beginning  of  tlie  chapter  it  was  re- 
marked that  to  give  the  plant  too  much  of  any  of  the 
things  it  requires  is  as  bad  as  to  give  it  too  little. 
This  is,  perhaps,  more  strikingly  seen  in  the  case  of 
heat  than  in  other  cases.  We  all  know  that  too  much 
heat  quickly  kills  both  animals  and  plants.  On  the 
other  hand,  if  they  have  too  little,  they  stop  growing, 
and  may  die. 

In  general,  the  less  water  the  plant  contains,  the 
more  resistant  it  is  to  cold.  This  is  well  shown  by  the 
behavior  of  greenhouse  plants;  excessive  watering 
makes  them  over- sensitive  to  heat  and  cold  (and  light 
as  well;  such  plants  are  liable  to  '■'  sunscald").  Plants 
which  have  just  been  transplanted  are  said  to  be  less 
sensitive  to  frost,  since  they  contain  less  water.  Frost 
does  not  injure  buds  in  winter  when  they  are  compara- 
tively dry,  but  in  spring,  when  they  are  full  of  sap,  it 
kills  them.  Frost,  during  the  period  when  sap  is  run- 
ning, causes  the  bark  to  adhere  to  the  wood,  and  it 
does  not  again  become  separable  until  the  return  of 
milder  weather.  In  such  cases,  the  health  of  the  tree 
may  not  always  be  affected;  but  the  crop  of  fruit  fails. 

Dry  seeds  which  contain  very  little  water  (about  10 
to  15  per  cent)"  stand  extremes  of  temperature  which 
would  kill  them  if  full  of  water.  Seeds  have  been  kept 
at  the  tempei^ature  of  liquid  hydrogen  (minus  238°  C, 
or  minus  396°  F.)  for  some  time,  and  carefully  thawed 
out  again,  when  they  grew  quite  normally. 


HOW    PLANTS    ARE    INFLUENCED  353 

The  way  in  which  a  frozen  plant  is  thawed  out 
makes  a  great  difference.  Allow  some  potatoes  to  freeze 
(they  may  be  easily  frozen  in  a  water-tight  can,  sub- 
merged in  a  mixture  of  pounded  ice  and  salt,  or  set  in 
an  ordinary  ice-cream  freezer).  Place  some  of  the 
frozen  potatoes  in  water  chilled  by  ice  (but  free  from 
salt) ,  and  let  them  stand  until  the  water  reaches  room 
temperature.  Place  others  at  once  in  a  warm  place,  so 
that  they  will  thaw  quickly. 

Frozen  leaves  (and  other  plant -tissues)  have  a 
peculiar  transparent  appearance  on  thawing  ;  the  same 
thing  occurs  when  they  are  boiled  in  water  or  injected 
with  water  in  an  air-pump  (see  page  190) ;  in  all  these 
cases  it  results  from  the  air-spaces  becoming  filled 
with  water.  It  is  supposed  that  when  a  plant  is 
allowed  to  thaw  rapidly  this  water  evaporates  and  that 
the  plant  suffers  injury,  which  might  be  avoided  by 
slow  thawing,  which  would  permit  the  cells  to  again 
absorb  the  water  which  escapes  from  them  into  the 
air  spaces  during  the  freezing. 

The  action  of  frost  on  the  trunk  may  result  in  long 
splits  in  the  trunk  or  in  the  killing  of  the  ends  of  the 
branches,  which  soon  turn  black.  The  best  treatment 
is  to  remove  the  injured  portions  by  priming  and  to 
direct  the  energies  of  the  tree  to  making  new  wood 
(prevent  it  from  bearing  fruit  for  a  season)  to  replace 
that  which  is  killed. 

Protection  from  frost  is   secured   by  covering  the 

w 


354 


EXPKItlMEyrS    WITH   PLANTS 


plauts  with  a  mulch,  or,  in  the  case  of  trees  and 
shrubs,  by  bending  them  down  (the  roots  must  be  cut 
in  such  a  way  as  to  permit  this)  on  the  approach  of 
winter  and  covering  them  with  straw  or  brushy 

Spraying  or  sprinkling  with  water  at  nightfall  is  a 
very  effective  means  of  protection  ;  this  depends  on 
the  fact  that  moisture  in  the  air  prevents  the  radiation 
of  heat  and  consequent  cooling  of  the  trees  and  soil ; 
it  acts,  so  to  speak,  as  a  trap  for  the  heat.    Filling  the 

air  with  dense  smoke 
from  bonfires  of  tar,  resin 
or  s  i  m  i  1  a  r  substances 
answers  the  same  pur- 
pose. 

The  pale  appearance 
of  young  leaves  during 
cold  weather,  which  is 
very  noticeable  in  Winter 
Wheat,  etc.  (see  Fig.  204 
of  the  Ivy  Geranium),  is 
due  to  the  fact  that  for 
the   formation  of  chloro- 


204.  Branch  of  Ivy  Genmium  after  a  few 
days  of  cold  weather;  the  young  leaves 
have  developed  without  being  able  to 
turn  green. 


phyll    a  higher  tempera- 
ture is  required  than  for 
growth.    The  leaves  con- 
sequently develop  but  cannot  turn  green. 

It  is  noticeable  that  some  kinds  of  plants  stand  far 

1  See  an  article  by  Galloway  in  the  Year  Book  of  the  U.  S.  Department  of 
Agriculture  for  1895. 


BOW    PLANTS    ARiJ    INFLUENCED  355 

more  cold  than  others  (just  as  some  kinds  stand  more 
water,  light  or  alkali  than  others).  Individual  plants 
vary  considerably  in  this  respect :  after  a  frost  which 
kills  most  plants  of  a  particular  species  it  is  often  pos- 
sible to  find  one  or  two  individuals  which  have  sur- 
vived, not  because  of  a  more  sheltered  position  but  by 
reason  of  their  greater  hardiness.  By  preserving  the 
seed  of  such  plants  and  selecting  seed  from  the  hardi- 
est plants  year  after  year,  hardy  varieties  may  be 
obtained. 

Of  equal  importance  with  hardiness  in  securing  va- 
rieties for  cold  regions  is  the  ability  to  ripen  quickly 
(earliness).  This  may  also  be  obtained  by  selection, 
as  has  happened  in  the  case  of  Wheat  in  the  United 
States;  as  a  result  the  Wheat  belt  has  moved  steadily 
northward,  especially  in  the  last  fifteen  years.  We 
have  a  record  of  one  case  in  which  a  winter  Wheat  was 
in  three  years  converted  into  a  summer  Wheat  in  this 
manner:  conversely,  in  three  years  a  summer  Wheat 
was  converted  into  a  winter  Wheat.  The  same  thing 
is  even  more  strikingly  true  of  Corn,  which  on  the 
plains  of  Santa  Fe  in  South  America  requires  six 
months  to  ripen,  while  in  the  Rainy  Lake  district  of 
Lake  Superior  it  ripens  in  two  months  and  a  half. 
This  great  change  has  all  been  accomplished  by  man. 

It  has  been  found  repeatedly  in  experiments  that 
cuttings  (of  the  same  kind  of  plant)  taken  from  a 
northern  region  and  placed  side  by  side  with  those  of 


356  EXPERIMENTS    WITH  PLANTS 

a  southern  region  develop  from  fifteen  to  twenty  days 
earlier  than  those  which  are  accustomed  to  the  warmer 
region.  Early  varieties  of  flowers,  etc.,  are  constantly 
imported  from  northern  points.  Temperature,  more 
than  anything  else,  determines  what  kinds  of  plants 
grow  in  a  given  region^.  The  tropics,  the  temperate 
and  the  arctic  zones  have  each  their  characteristic 
vegetation.  Plants  which  flourish  in  the  tropics  may 
be  cultivated  in  the  temperate  zone  (e.  g..  Date  Palm, 
Rubber  Plant,  etc.),  but  remain  stunted  and  refuse  to 
bear  fruit.  The  study  of  the  various  zones  to  be  found 
in  a  country  is  very  important  in  determining  what 
part  is  best  adapted  for  various  crops. ^ 

Wherever  there  are  high  mountains  there  are 
opportunities  to  study  these  zones  to  great  advantage, 
since  as  we  ascend  the  mountain  we  pass  through 
successive  zones.  It  will  then  be  seen  how  much 
depends  on  exposure;  i.  e.,  the  southern  face  of  the 
mountain  being  so  much  w^armer  than  the  northern, 
the  zones  will  run  higher,  etc.  The  same  may  be  seen 
in    even    a   small    hill   or  elevation.    For   this    reason 

lAn  interesting  illustration  of  this  is  seen  in  the  forests  of  the  United 
States  and  Canada.  As  ws  go  northward  from  Florida  we  find,  considering  only 
good  and  well-watered  soils,  that  the  hardwood  forest  gradually  diminishes, 
both  in  the  number  of  trees  and  the  number  of  kinds  represented,  until  we  come 
to  the  great  pineries  of  the  northern  United  States  and  Canada.  Still  further 
north  these  are  succeeded  by  Birch,  Willow  and  Alder:  these  gradually  dim- 
inish northward  until  we  roach  the  treeless  wastes. 

2  The  "  Crop  Zones  "  of  the  United  States  are  now  being  determined  by  the 
United  States  Biological  Survey. 


HOW   PLAINTS    ABE    INFLUENCED  357 

the  "lay  of  the  land"  is  very  important  for  plants. 
It  often  happens  that  one  side  of  a  valley  yields  good 
crops,  while  the  opposite  side  is  valueless  for  cultiva- 
tion. 

It  is  interesting  to  notice  that  during  the  day  the 
hillside  (especially  the  southern  and  southwesterly 
exposure)  i^  warmer  than  the  valley  (except  when  a 
cold  wind  blows) ;  the  same  is  true  at  night,  for  the 
cold  air,  being  heavier,  sinks  down  into  the  valleys, 
so  that  they  often  have  frost  at  night  when  the  hill- 
sides above  are  exempt  from  it. 

Plants  which  grow  in  high  altitudes  have  stunted 
stems  with  limbs  densely  branched  or  hugging  the 
ground  in  the  form  of  rosettes.  These  features  have 
been  produced  experimentally  to  a  certain  extent  by 
growing  ordinary  plants  under  favorable  conditions 
by  day  and  keeping  them  in  an  ice-house  during  the 
night.  This  imitates  natural  conditions,  since  the 
plants  in  question  are  comparatively  warm  during  the 
day  when  the  sun  is  shining,  but  cool  off  very  rapidly 
after  sunset  and  remain  cold  during  the  night. 
Normally  the  greatest  growth  takes  place  at  night, 
hence  chilling  them  at  this  time  explains,  in  part  at 
least,  their  stunted  growth. 

Alpine  plants  have  very  commonly  larger  and 
brighter  colored  flowers,  which  are  also  richer  in 
honey,  so  that  the  mountains  are  particularly  good  for 
bee-keepers.    The  foliage  of  these  plants  shows  many 


358  A'Xj'h'h'iMh'yrs   with  plants 

of  the  same  devices  for  preventing  evaporation  which 
we  have  seen  in  desert  plants  :  the  strong  light,  rare- 
fied air  and  the  constant  winds  tend  to  promote 
evaporation,  while  the  coldness  of  the  ground  hinders 
absorption . 

Owing  to  the  short  time  which  such  plants  have 
for  flowering  and  fruiting,  they  perform  these  opera- 
tions very  rapidly,  often  in  half  the  time  needed  by 
similar  species  in  the  lowlands. 

The  plants  of  northern  latitudes  resemble  alpine 
plants  in  most  respects,  and  especially  in  the  last- 
mentioned  feature,  i.  e.,  early -flowering  and  fruiting. 
Gardeners  take  advantage  of  this  to  get  early  varie- 
ties by  importing  seed  from  northern  regions.  Some- 
times seed  is  sent  to  such  regions  to  be  grown  until 
the  desired  earliness  has  been  obtained. 

Of  the  plants  familiar  to  you,  which  are  most  sensi- 
tive to  cold?  which  are  least  sensitive !  Do  you  find 
differences  in  individual  branches  of  the  same  tree  in 
this  respect? 

In  view  of  the  facts  which  we  have  just  discussed, 
we  may  realize  vividly  that  the  life  of  every  plant  is  a 
continual  and  delicate  adjustment  to  its  surroundings. 
Some  plants  possess  the  power  of  adjustment  to  a 
greater  degree  than  others;  but  all  must  exercise  it 
constantly  in  order  to  survive;  and  this  is  a  funda- 
mental characteristic  of  all  living  organisms. 

We  may  illustrate  this  further  by  considering  a  tree. 


HOW    PLANTS    AKE    INFLUENCED  359 

It  is  a  very  exact  index  of  its  surroundings,  so  that  a 
skilful  woodsman  knows  at  once,  on  looking  at  it,  the 
conditions  under  which  it  has  grown.  The  influence  of 
light,  water,  prevailing  winds,  have  all  left  their  marks 
on  it.  Its  position,  with  reference  to  the  compass,  can 
be  told  by  examining  it.  For  this  reason,  in  transplant- 
ing a  tree,  we  should  be  careful  to  set  it  so  that  the 
same  side  faces  the  north  after,  as  before  its  removal. 

These  facts  serve  to  show  that  the  form  of  the  plant 
is  largely  determined  by  its  surroundings.  It  may  also 
be  greatly  changed  by  diseases,  especially  the  attacks 
of  fungi,  to  which  are  due  the  remarkable  growths 
known  as  "witches'  brooms,"  etc.,  as  well  as  by  in- 
sects, which  not  only  cause  the  formation  of  all  sorts 
of  curious  galls,  but  even  in  some  cases  produce  the 
greening  of  flowers,  in  which  the  petals,  anthers,  etc., 
are  transformed  into  green,  leaf- like  bodies. 

Moreover,  the  development  of  each  part  of  the  plant 
is  influenced  by  that  of  every  other,  as  is  demonstrated 
every  day  by  the  experience  of  making  cuttings  and 
of  pruning  (see  pages  79,  ^^^  257  and  263).  If  the  tip 
of  the  main  axis  of  a  Pine  be  removed,  the  branches 
just  below  it  begin  to  straighten  up  to  take  its  place; 
one  finally  does  so  and  the  rest  then  fall  back  to  their 
original  positions;  the  one  which  becomes  upright 
changes  its  structure  and  becomes  like  the  tip  of  the 
main  trunk  whose  place  it  takes,  e.  g.,  it  becomes 
alike  on  all  sides  (and  the  intenuil  structure  changes. 


360  EXPERIMENTS    WITH  PLANTS 

accordingly)  instead  of  having  an  upper  and  a  lower 
side  (with  a  corresponding  difference  in  internal  struct- 
ure). The  Potato  furnishes  another  illustration;  if  the 
young  tubers  be  cut  off  as  they  are  forming,  the  tuber- 
forming  material  accumulates  in  the  parts  above 
ground  and  produces  tubers  in  the  branches;  these  are 
green  and  bear  leaves.  Try  both  these  experiments,  if 
possible. 

This  influence  of  one  part  on  another  is  called  cor- 
relation. Numerous  other  illustrations  might  be  given; 
it  will  suffice  to  mention  the  effect  which  the  fertiliza- 
tion of  the  ovary  has  on  surrounding  parts  (see  page 
309) .  Experiments  on  this  point  may  easily  be  made 
by  removing  the  anthers  in  the  bud  and  preventing 
pollination  by  paper  bags. 

It  is  hoped  that  the  facts  set  forth  in  this  chapter 
will  lead  to  experiments  when  practicable,  and  to  con- 
stant observation  of  the  experiments  which  are  every- 
where   spontaneously   occurring    in    garden  and  field. 


CHAPTER   IX 

PLANTS    WHICH    CAUSE    DECAY,    FERMENTATION 
AND    DISEASE 

What  is  the  cause  of  decay  ?  Formerly  it  was  sup- 
posed to  be  due  to  some  property  residing  in  the 
organism  itself ;  our  present  knowledge  is  that  it  is 
due  to  plants  called  bacteria.  Although  too  minute  to 
be  seen  except  with  the  microscope,  they  can  neverthe- 
less be  studied  with  the  simplest  apparatus. 

To  beghi  with,  we  may  get  an  abundant  growth  of 
bacteria  by  putting  a  little  hay  in  water  and  allowing 
it  to  stand  a  few  days,  when  the  bacteria  will  form  a 
gelatinous  film  on  the  surface.  On  mounting  a  drop  of 
this  in  water  on  a  slide  and  examining  it  under  the 
microscope,  the  bacteria  appear  as  very  small,  glisten- 
ing bodies  approaching  in  shape  some  of  the  forms 
shown  in  Fig.  205;  very  probably  some  of  these  will 
be  in  motion.  This  motion  may  be  merely  mechan- 
ical, i.  e.,  a  dancing  motion  such  as  any  small  particles 
(e.  g.,  India  ink  or  vermilion)  show  in  a  liquid,  or  it 
may  be  due  to  the  activity  of  the  bacteria,  which  move 
by  means  of  whip-like  protoplasmic  projections  (cilia). 
Pour  off  some  of  the  liquid  in  which  the  bacteria  are 

(361) 


362 


expj!:kiments  with  plants 


growing,  strain  it  through  a  cloth,  and  fill  five  vials 
or  bottles  almost  half  full  of  it.  Insert  in  the  mouth 
of  each  vial  (or  bottle)  a  firm  cotton   plug   made  by 


[o. 


205.  Different  kinds  of  bacteria:  (a)  spherical  bacteria  imbedded  in  a  gelati- 
nous film  which  floats  on  the  surface  of  the  liquid,  (6)  rod-like  forms,  (c)  bac- 
teria multiplying  by  division  into  two,  {d)  bacteria  of  lock-jaw  (tetanus),  with 
a  spore  at  one  end,  ie)  elongated  rods,  (/)  rod-like  forms  dividing,  {g)  rod- 
like forms  with  a  spore  in  each,  (h)  spiral  forms. 

rolling  the  cotton  into  a  firm  roll  just  large  enough  to 
fit  the  vial.  Place  one  of  the  bottles  {a)  in  a  warm 
place  in  the  light,  another  {h)  in  a  warm  place  in  the 
dark,  another  (c)  in  a  cool  place  (preferably  on  ice) 


PLANTS    WHICFT    OAirSi:    DECAY 


363 


in  the  dark.  Into  the  fourth  bottle  {d)  put  a  drop  of 
formalin,  and  place  alongside  of  (b) .  The  fifth  bot- 
tle {e)  we  will  subject  to  the  heat  of  steam.  This  is 
most  conveniently  done  by  placing  the  bottles  in  a 
pan  and  inverting  another  pan 
over  it  as  a  cover,  or  by  means  of 
the  apparatus  shown  in  Fig.  206. 
It  consists  of  a  pail  (six  to  eight 
inches  in  diameter)  and  two  pans, 
all  preferably  of  graniteware  (tin 
may  be  used) .  One  pan  serves  as 
a  cover,  while  the  other,  which  is 
pierced  with  holes,  serves  as  a 
support.  A  little  water  is  put  into 
the  pail,  and  it  is  then  set  on  a 
stove  or  over  a  burner.  The  vials 
or  other  dishes  are  placed  on  the 
support,  the  cover  is  fitted  on  and 
the  water  is  allowed  to  boil.  When  it  has  boiled  for 
half  an  hour  we  remove  the  vials.  This  process  is 
known  as  sterilizing  (the  apparatus  is  called  a  steam 
sterilizer).  We  place  the  sterilized  vials  in  a  warm 
place  in  the  dark,  and  renew  the  sterilizing  each  day 
until  they  have  been  sterilized  three  days  in  succession. 
Examine  all  of  the  vials  every  day.  In  which  does 
the  most  rapid  growth  of  bacteria  occur,  as  shown 
by  the  cloudiness  of  the  liquid  and  the  formation 
of  a  surface  film? 


206.  Steam  sterilizer,  consist- 
ing of  a  pail,  a  pan  for 
cover  and  a  smaller  pan 
pierced  with  holes  as  a  sup- 
port (all  should  be  of  tin 
or  agateware).  (Sectional 
view.) 


364  EXPERIMENTS    WITH   PLANTS 

Bacteria  in  general  grow  best  at  from  80°  to  95°  F. 
Below  40°  F.  and  above  110°  F.  they  make  practically 
no  growth.  The  temperature  of  ice  fails  to  kill  many 
kinds;  even  that  of  liquid  air  (minus  310°  F.)  does  not 
kill  all  kinds. 

Bright  light  kills  many  kinds,  while  others  are  not 
much  affected  by  it. 

Formalin  is  a  good  example  of  a  disinfectant  which 
kills  the  bacteria.  (Disinfectants  which  kill  the  germs 
are  called  germicides,  those  which  thoroughly  check 
their  growth  or  stop  it  are  called  antiseptics.)  One  part 
in  5,000  or  10,000  of  water  is  said  to  be  efficacious 
against  many  bacteria;  articles  may  be  disinfected  by 
leaving  them  for  a  few  hours  in  a  closed  box  exposed 
to  formalin  vapor,  or  sulphur  may  be  burned  in  any 
closed  space  with  good  results.  Other  chemical  dis- 
infectants are  chloride  of  lime,  corrosive  sublimate, 
carbolic  acid,  potassium  permanganate,  strong  mineral 
acids,  ete.^ 

The  effect  of  sterilization  is  due  to  the  fact  that  bac- 
teria in  their  ordinary  or  vegetative  condition  are  killed 
by  the  heat  of  steam.    Some  of  the  bacteria  found  in 

iThe  following  will  serve  to  indicate  approximately  the  strength  to  be 
used  :  Carbolic  acid  3  per  cent  or  one  tablespoonful  of  the  ordinary  solu- 
tion to  a  pint  of  water;  lysol  1  to  2  per  cent;  copper  sulphate  1  to  2  per  cent; 
chloride  of  lime  3  per  cent;  potassium  permanganate  1  to  2  per  cent  (useful 
as  deodorizer  also);  corrosive  sublimate  one-tenth  of  1  per  cent;  hydrogen 
peroxide  nearly  full  strength;  listerine  full  strength.  Wounds  should  be  well 
washed  with  disinfectant  solution  by  means  of  a  pipette  and  then  covered  with 
iodoform,  or  powdered  boracic  acid. 


PLANTS    WHICH    CAUSE    DECAY 


365 


hay  infusions  produce  resistant  bodies  known  as 
spores  (compare  Fig.  205,  g)  which  are  not  killed  by 
this  temperature.  On  standing  a  few  hours  the  spores 
germinate  and  pass  into  the  vegetative  condition,  when 
they  may  be  killed  by  steam  heat.  Hence  the  value 
of  sterilizing  on  three  successive  days.  Ordinarily, 
however,  one  sterilization  of  half  an  hour  answers 
every  purpose. 

It  was  formerly  supposed  that  the  growth  which 
occurs  in  infusions,  etc.,  was  due  to  spontaneous 
generation,  i.  e.,  to  the 
origin  of  living  organisms 
from  lifeless  matter.  This 
view  received  confirma- 
tion from  the  fact  that  an 
infusion  may  be  boiled 
and  growth  nevertheless 
occur.  With  the  discov- 
ery of  resistant  spores 
and  of  the  fact  that  after 
several  sterilizations  no 
growth  occurs,  the  doc- 
trine of  spontaneous 
generation  was  over- 
thrown. 

Let  us  now  take  three  tumblers,  place  a  slice  of 
boiled  potato  in  each,  cover  with  cotton  held  in  place 
by  an   elastic    band    as    shown    in    Fig.    207   (or  use 


207.  Tumbler  containing  a  slice  of  boiled  po- 
tato, closed  by  a  cotton  plug  held  in  place 
by  an  elastic  band. 


366  EXPERIMENTS    WITH    PLANTS 

small  tumblers  and  insert  a  cotton  plug  as  in  Fig.  212) 
and  sterilize  them  all  for  half  an  hour.  After  they 
have  cooled  down  again,  remove  the  cotton  from  one 
{a),  expose  to  the  air  for  a  minute  and  replace  the 
cotton  :  to  another  (6),  transfer  a  minute  quantity  of 
bacteria  from  the  liquid  by  means  of  a  needle  J 
For  this  purpose  we  pass  the  needle  back  and  forth 
several  times  through  the  flame,  and  when  cool  dip  it 
into  the  liquid.  We  now  lift  the  cotton  at  the  edge 
and  draw  the  needle  once  across  the  surface  of  the 
potato  and  at  once  replace  the  cotton.  Leave  the 
third  tumbler  (c)  intact,  as  a  control. 

Put  all  the  tumblers  away  in  a  warm  place  in  the 
dark  and  observe  them  daily.  The  bacteria  in  {a) 
come  from  the  air  ;  many  disease -producing  bacteria 
(e.  g.,  those  of  tuberculosis)  are  wafted  about  in  the 
air;  for  this  reason  consumptives  should  take  special 
precautions  to  avoid  infecting  the  air.  Do  the  spots  of 
decay  appear  in  {h)  anywhere  except  along  the  needle 
track:  do  any  appear  in  (c)?  Does  the  potato  beneath 
the  spots  alter  in  color,  consistency,  etc.?  Scrape  a  bit 
of  the  potato  from  one  of  these  spots,  mount  the  scrap- 
ing in  a  drop  of  water,  and  examine  under  the  micro- 
scope. The  large,  glistening  bodies  are  starch  grains, 
while  the  bacteria  appear    as  minute  bodies  floating 

1  This  is  prepared  by  heating  the  end  of  a  glass  rod  in  a  flame  until  it  fuses 
and  then  forcing  into  it  a  piece  of  fine  steel  (or  platinum,  if  obtainable)  wire 
about  two  inches  long. 


PLANTS    WHICH    CAiSlJ    DEC  AT 


367 


208, 


about  in  the  liquid  (Fig.  208).    Add  a  drop  of  iodine 
solution,  and  observe. 

Wo  may  get  a  good  idea  of  the  relative  size  of  the 
bacteria  by  comparing  them  witii  the  starch  -  grains, 
which  latter  are  too  small  to 
be  distinctly  visible  to  the 
naked  eye  but  are  easily  seen 
with  a  hand- lens. 

Do  you  find  that  the  spots 
on  the  potato  differ  in  color, 
consistency,  shape  and  gen- 
eral appearance?  If  so,  they 
are,  in  all  probability,  due  to 
different  kinds  of  bacteria.  In 
order  to  separate  the  various 
kinds,  we  may  proceed  as 
follows:  Fill  a  vial  half  full  of  distilled  water,  and 
sterilize  for  half  an  hour.  Then  pass  the  needle  through 
the  flame  two  or  three  times ;  when  cool  touch  it  to  the 
spot  from  which  a  culture  is  desired,  and  stir  it  about 
in  the  vial.  Remove  the  needle,  sterilize  in  the  flame, 
and  then  dip  it  in  the  vial  again  and  touch  it  to  a  pre- 
viously sterilized  slice  of  potato  (arranged  as  before  in 
a  tumbler),  at  various  points  a  little  distance  apart, 
and  at  once  replace  the  cotton.^  If  the  amount  of  water 
used  is  sufficient,  the  bacteria  will  be  so  scattered  that 

1  During  this  operation  the  tumbler  should  be  held  nearly  horizontal,   to 
keep  bacteria  from  falling  upon  the  potato  from  the  air. 


.  A  scraping  from  a  potato  culture, 
showing  starch-grains  and  bacteria. 
A  good  way  to  get  an  idea  of  the 
size  of  bacteria  is  by  comparing 
them  with  some  well-known  object, 
such  as  a  starch-grain. 


368  EXPERIMENTS    WITH  PLANTS 

each  minute  drop  of  the  liquid  will  contain  not  more 
than  one  of  them,  so  that  whene\'er  we  touch  the  potato 
we  shall  deposit  not  more  than  one;  hence  each  spot 
will  be  the  result  of  the  growth  of  a  single  bacterium: 
this  is  a  pure  colony:  if  we  infect  a  sterilized  potato 
(or  other  medium)  from  such  a  colony,  so  as  to  get 
only  one  kind  of  bacterium  in  the  culture,  we  obtain  a 
pure  culture. 

It  is  interesting  to  consider,  in  connection  with  this 
mode  of  propagation,  that,  as  long  as  an  individual 
keeps  on  dividing,  there  can  be  no  such  thing  as  death 
from  old  age,  since  the  parent  is  completely  absorbed 
into  the  offspring. 

Bacteria  are  distinguished  not  so  much  by  their  forrn 
and  general  appearance  under  the  microscope  as  by 
their  behavior  when  grown  on  various  substances,  such 
as  potato,  gelatine,  beef -broth,  etc.  They  are  classified 
largely  according  to  the  size,  shape,  consistency,  color, 
etc.,  of  the  spots  or  colonies  which  they  produce. 

One  very  interesting  form,  which  may  be  easily 
recognized,  appears  frequently  on  potato  and  bread - 
cultures:  it  is  bright  red  in  color,  and  is  of  especial 
interest  as  causing  the  "  bloody- bread"  of  the  middle 
ages,  which  was  believed  to  bleed  miraculously. 

The  bacteriological  examination  of  water  is  so  im- 
portant and  at  the  same  time  so  simple  that  we  may 
well  turn  our  attention  to  it.  For  this  purpose  we  may 
prepare  some  nutrient  gelatin  as  follows:  Make  some 


PLANTS    WHICH    CAUSE    DECAY 


369 


beef- broth  by  heating  a  pound  of  chopped  beef  for  half 
an  hour  (at  about  65°  C)  in  a  pint  of  water.  Strain  it 
through  a  cloth,  and  add  two  ounces  of  gelatin  (the 
"  sparkling  gelatin  "  used  in  cooking  is  preferable) ,  and 
let  it  soak  over  night.  In  the  morning,  heat  in  the 
sterilizer  until  dissolved,  then  add  one-tenth  ounce  salt 
(best  accomplished  by  adding  one  ounce  salt  to  100  c.c. 
of  water,  and  taking  10  c.c.  of  this) 
and  one -fifth  ounce  peptone  (obtain- 
able at  drug- stores;  it  may  be  omitted 
if  necessary) ,  add  a  tablespoonful  of 
molasses  and  finish  by  adding  dilute 
lye  or  lime-water  until  the  gelatin  is 
slightly  alkaline  to  litmus.  Remove 
the  neck  from  a  funnel  so  that  it  will 
fit  into  a  tumbler  (Fig.  209),  and 
filter  the  gelatin  through  filter  paper 
or  cotton,  keeping  the  whole  hot  in 
the  sterilizer  during  the  process.  If 
the  gelatin  does  not  appear  clear, 
filter  again,  first  beating  in  a  little  white  of  ^gg. 
It  may  then  be  placed  in  a  bottle  and,  the  neck  be- 
ing plugged  with  cotton,  sterilized.  If  necessary,  re- 
peat this  for  three  successive  days,  when  it  will  keep 
indefinitely.  (Each  time  the  bottle  is  opened  it  must 
be  sterilized  again.)  Now  obtain  several  flat- sided 
bottles  of  the  same  size,  and  put  into  each  sufficient 
gelatin  to  cover  the  side  when  the  bottle  is  flat  on  the 


209.  Funnel  with  neck  re- 
moved so  as  to  fit  into 
a  tumbler:  the  whole 
is  placed  in  the  steri- 
lizer, in  case  gelatin 
is  to  be  filtered  hot. 


210.    Flat  bottle  containing  gelatin:  used  for  "plate  cultures." 


370  EXPERIMENTS    WITH    PLANTS 

table  (Fig.  1210) .  The  same  amount  should  be  placed 
in  each  bottle;  this  is  easily  managed  with  a  sterilized 
pipette  or  medicine -dropper.   Wipe  the  mouth  and  neck 

of  each  bottle, 
and  plug  with 
cotton ;  then 
sterilize  and 
set  aside  for  a 
day  or  two.  If 
no  bacterial  growth  appears,  we  may  proceed.  Warm 
the  bottle  just  enough  to  liquefy  the  gelatin,  remove 
the  plug,  and  introduce  (by  means  of  a  sterilized  pi- 
pette or  medicine -dropper)  the  same  quantity  of  water 
(several  drops)  into  each  bottle  (a  separate  sterilized 
pipette  must  be  used  for  each) .  Replace  the  plug, 
mix  the  contents  by  turning  the  bottle  from  side  to  side 
(do  not  allow  gelatin  to  get  on  the  plug)  and  place  the 
bottle  on  its  side  in  a  dark  place.  Such  cultures  are 
called  plate  cultures,"  and  they  serve  excellently  to  tell 
how  many  bacteria  the  water  contains,  since  we  may 
count  the  colonies  which  come  from  a  given  quantity 
of  water  (in  this  case  we  assume  that  each  colony 
comes  from  a  single  bacterium). 

It  is  well,  in  making  this  experiment,  to  compare 
some'  water  from  the  drinking  supply,  some  from  a 
stagnant  pond  or  pool  and  some  from  a  barnyard.  In 
the  latter  case  we  shall  probably  find  bubbles  of  gas 
torming  in  the  gelatin.    This  is  an  mdication  of  the 


PLANTS    WHICH    CAUSE    DECAY  371 

colon  bacillus  which  is  characteristic  of  animal  excre- 
ment, and  when  found  in  water  shows  sewage  contami- 
nation; such  water  should  not  be  drunk  without  being 
boiled,  and  a  sample  should  be  taken  to  the  health 
officer  for  examination. 

One  fact  which  cannot  help  striking  us  in  observing 
these  cultures  is  the  rapidity  with  which  the  bacteria 
grow.  A  single  bacterium  produces  in  forty-eight  hours 
a  spot  or  colony  containing  thousands  on  thousands. 
If  we  observe  the  bacteria  in  a  hanging  drop  (see  Fig. 
165)  under  the  microscope  we  can  see  the  manner  in 
which  they  multiply :  it  consists  in  simply  dividing  into 
two  as  shown  in  Fig.  205  (c).  It  has  been  observed  that 
this  division  into  two  may  occur  as  often  as  once  every 
half -hour;  if  this  rate  could  be  maintained  for  twenty- 
four  hours  and  none  should  die,  we  should  have  at  the 
end  of  that  time  more  than  two  hundred  and  eighty 
trillions  of  descendants  from  a  single  germ.  It  may 
be  readily  realized  that  even  at  a  much  less  rapid  rate 
of  increase  a  few  typhoid  germs  might  soon  infect  a 
whole  water  supply. 

In  the  bacteriological  examination  of  water,  it  is 
customary  to  count  the  bacteria  by  the  method  just 
described,  and  also  to  examine  for  the  colon  bacillus 
and  for  disease -producing  bacteria,  such  as  those  of 
typhoid,  cholera,  etc.  These  are  identified  by  their 
appearance  in  the  cultures  and  under  the  microscope. 

It  is  important  to  know  that  typhoid  may  be  con- 


372  EXPERIMENTS    WITH  PLANTS 

tracted  by  eating  raw  oysters,  which  are  frequently 
grown  in  water  contaminated  by  sewage. 

Fig.  211  shows  the  distribution  of  cholera  cases  in 
the  Hamburg  epidemic  of  1892.  It  will  be  noticed  that, 
in  the  words  of  Professor  Koch,  "cholera  went  right  up 
to  the  boundary  of  Altona  and  there  stopped.  In  one 
street,  which  for  a  long  way  forms  the  boundary,  there 
was  cholera  on  the  Hamburg  side,  whereas  the  Altona 
side  was  free  from  it."  This  is  equally  true  when  the 
boundary  runs  diagonally  through  a  block.  The  ex- 
planation lay  in  the  fact  that  while  both  cities  used  the 
same  water  supply  (which  received  raw  sewage  from 
several  towns) ,  Altona  filtered  the  water  carefully,  while 
Hamburg  did  not. 

The  filtration  of  water  is  a  very  simple  process.  It 
is  passed  through  several  feet  of  sand  (sometimes 
mixed  with  charcoal)  and  a  film  soon  forms  on  the  sur- 
face of  the  sand  which  catches  the  bacteria.  Such  a 
film  may  be  artificially  produced,  if  necessary,  by  add- 
ing chemicals  (e.  g.  alum)  to  the  water  without  injur- 
ing it  for  drinking  purposes.  Every  town  or  city  water 
supply  should  be  filtered;  the  cost  is  slight  and  the 
benefits  very  great.  The  small  filters  sold  for  house- 
hold use  are  for  the  most  part  highly  injurious  and 
serve  only  as  breeding  places  for  bacteria,  owing  to  the 
fact  that  they  cannot  be  properly  cleaned. 

Let  us  now  examine  some  milk.  Fill  three-  vials 
half  full  of  nutrient  gelatin,   plug,  sterilize,  and  set 


374  EXPERIMENTS    WITH  PLANTS 

aside  for  two  or  three  days,  and  if  no  growth  appears, 
proceed  to  roake  a  bacteriological  examination  of  milk. 
For  this  purpose  obtain  some  milk  freshly  drawn; 
some  milk  which  has  stood  for  from  twelve  to  twenty - 
four  hours,  and  some  sour  milk.  Make  so-called  "stab 
cultures "  by  dipping  the  point  of  the  sterilized  needle 
into  the  milk,  and  then  plunging  it  straight  down 
through  the  center  of  the  gelatin  to  the  bottom;  the 
needle  must  be  sterilized  in  the  flame  after  each  stab. 
The  plugs  should  be  replaced  at  once,  and  the  vials 
set  aside.  In  which  do  you  see  the  first  signs  of 
growth;  in  which  is  the  growth  most  abundant;  what 
do  you  conclude  as  to  the  relative  number  of  bacteria 
in  the  three  kinds  of  milk  ? 

Stab  cultures  are  especially  interesting  because  some 
of  the  bacteria  are  placed  deep  in  the  gelatin  w^here 
they  are  deprived  of  air,  while  others  are  left  on  the 
surface.  Some  kinds  of  bacteria  die  if  deprived  of  air; 
other  kinds  die  if  exposed  to  the  air,  while  there  are 
still  other  kinds  which  can  live  under  either  condition. 
In  a  stab  culture  we  have  an  opportunity  to  judge 
which  of  these  classes  of  bacteria  w^e  have.  Thus,  a 
culture  which  grows  like  Fig.  212  (a),  indicates  the 
first  class;  if  like  Fig.  212  (&),  the  second  class;  if 
like  Fig.  212  (c) ,  the  third  class  (or  a  mixture  of  the 
first  two). 

In  order  to  determine  whether  bacteria  use  up  oxygen 
and  produce  carbon  dioxide,  we  may  take  an  infusion 


PLANTS    WHICH    CAUSE    DECAY 


375 


which  is  filled  with  bacteria,  place  it  in  a  wide -mouthed 
bottle,  and  place  in  it  a  vial  containing  clear  water, 
and  stopper  the  larger  bottle  as  shown  in  Fig.  30.  As 
a  control,  use  a  similar  arrangement  with  pure  water 
in  place  of  the  infusion.    A  still  better  arrangement  is 


kirn 


tllLl 


212.  Stab  cultures  in  gelatin:  (a)  air-loving  bacteria,  (6)  bacteria  not  able  to 
grow  in  the  presence  of  air,  (c)  bacteria  which  grow  equally  well  with 
or  without  air. 

to  repeat  the  experiment  described  on  page  34,  Fig. 
31,  using  the  infusion  in  place  of  the  seeds. 

Wo  may  now  place  some  milk  in  vials  or  bottles, 
close  the  mouths  with  cotton,  and  sterilize  for  ten 
minutes  on  three  successive  days.  Open  one  bottle 
three  days  after  the  last  sterilization,  another  a  week 
later,  and  another  two  weeks  later.    Do  you  detect  any 


376  EXPERIMENTS    WITH  PLANTS 

sigD  of  souring  ?  It  appears  that  the  souring  of  milk  is 
d):<e  to  bacteria. 

Our  stab  cultures  have  shown  us  that  while  there 
are  comparatively  few  bacteria  in  perfectly  fresh  milk, 
they  increase  very  rapidly,  so  that  after  standing  a  few 
hours  the  milk  is  full  of  them.  Some  of  these  bacteria 
cause  the  souring  of  milk,  others  impart  disagreeable 
flavors  and  odors  (if  the  milk  is  allowed  to  stand  long 
enough) ;  some  seem  to  have  no  effect  on  the  milk, 
while  still  others  produce  the  agreeable  flavor  of  butter 
and  cheese.  These  latter  may  be  procured  in  pure  cul- 
tures by  dairymen,  and  added  to  their  butter  or  cheese 
to  produce  the  desired  flavor. 

In  milk  may  occur  bacteria  which  produce  typhoid, 
diphtheria,  scarlet  fever,  cholera,  tuberculosis  (dis- 
puted), and  intestinal  troubles  (cholera  infantum). 
The  infection  may  come  from  the  cow,  from  the  people 
who  handle  the  milk,  or  from  water.  In  Stamford, 
Connecticut,  there  occurred  in  1895,  386  cases  of 
typhoid,  of  which  97  per  cent  were  on  the  route  of  one 
milkman  who  rinsed  his  cans  in  cold  water  from  a 
polluted  well.  Milk -cans  and  utensils  should  be  care- 
fully sterilized,  and  scrupulous  cleanliness  both  of  the 
animals  and  the  persons  who  handle  the  milk  is  highly 
desirable. 

In  order  to  keep  milk  from  souring,  it  may  be 
boiled,  by  which  process  the  bacteria  are  mostly  killed; 
but  since  many  persons  find  the  flavor  of  boiled  milk 


PLANTS    WHICH    CAUSE   DECAY  377 

disagreeable,  it  is  preferable  to  pasteurize^  it,  i.  e.,  to 
place  the  bottle  of  milk  in  water  which  is  heated  to  155"^ 
F.  for  twenty  minutes,  and  then  cooled.  In  practice  it 
is  usually  more  convenient  to  heat  the  water  to  155°  F. 
and  then  set  it  aside  to  cool  slowly.  Treat  several 
bottles  of  milk  in  this  way  (they  should  be  stoppered 
with  cotton,  or  well  corked).  How  long  does  it  keep 
sweet  (a  bottle  once  opened  must  be  discarded) ;  do 
you  detect  any  unpleasant  flavor  due  to  the  heating  ? 

Pasteurizing  is  a  legitimate  process,  but  the  use  of 
formalin  and  other  preservatives  by  milkmen  is  to  be 
strongly  condemned  ;  milk  so  treated  is  especially 
harmful  to  infants.  A  rough  test  for  formalin  which  is 
sometimes  used  is  as  follows :  Pour  ordinary  com- 
mercial (impure)  sulphuric  acid  slowly  into  a  glass  of 
milk,  letting  it  run  down  the  side  of  the  glass.  If  a 
purple  color  appears  at  the  junction  of  the  milk  and 
acid  it  indicates  the  presence  of  formalin,  and  the 
milk  should  be  taken  to  the  health  officer  for  a  test. 
Put  a  little  formalin  in  some  pure  milk  and  make  the 
test :   how  great  a  dilution  will  give  the  test  ? 

We  notice  that  the  sulphuric  acid  curdles  the  milk  : 
this  is  due  to  the  fact  that  the  milk  contains  a  proteid 
called  casein,  which  (like  the  white  of  an  Qgg)  is 
coagulated  by  acids  (cheese  is  made  from  the  casein 
of  the  milk).    The  curdling  of  milk  is  caused   by  an 

^  See  an  article  in  the  Year-Book  of  the  U.  S.  Dept.  of  Agriculture  for  1894 
by  Schweiuitz;  for  1895  by  Moore. 


378  EXPERIMENTS    WITH  PLANTS 

acid  (lactic  acid)  produced  by  bacteria  which  change 
the  sugar  of  the  milk  into  lactic  acid  (test  some  sour 
milk  with  litmus).  After  a  time  this  process  ceases, 
long  before  the  milk-sugar  is  all  used  up,  because  the 
acid  checks  the  activity  of  the  bacteria.  If  we  now  add 
enough  lime-water  to  neutralize  the  acid,  they  will 
begin  to  grow  and  form  more  acid,  as  you  will  see  on 
testing  with  litmus  paper  a  few  hours  later.  Make 
this  test.  It  is  a  general  rule  that  both  animals  and 
plants  are  poisoned  by  their  own  excretions. 

When  bacteria  live  in  the  bodies  of  animals  or 
plants,^  they  are  dangerous  or  harmless  according  as 
their  excretions  are  poisonous  or  not  to  the  organism 
in  which  they  live.  It  is  well  known  that  the  human 
body  contains  many  bacteria  which  are  perfectly  harm- 
less, because  their  excretions  are  not  poisonous  to 
it.  On  the  other  hand,  the  poisonous  excretions 
(known  as  toxins)  of  other  sorts  may  produce  death 
in  a  few  hours  (as  in  lockjaw,  etc.).  It  is  not  neces- 
sary that  the  bacteria  should  enter  the  body  at  all ;  if 
their  toxins  are  introduced  into  the  body  the  same 
effect  is  produced  as  if  the  bacteria  themselves  were 
present.  Bacterial  diseases  would  invariably  cause 
death  wherever  they  obtained  a  foothold  were  it  not 
for  the  fact  that  the  body,  when  the  toxins  make  their 
appearance    in    it,    produces    antitoxins^    e.    g.,    sub- 

^  Very  few  bacteria  are  known  which  can  live  when  injected  into  a  live 
plant;  in  most  cases  they  die  in  a  few  hours. 


PLANTS    WHICH    CAUSE    DECAY  379 

stances  which  neutralize  the  effect  of  the  toxins  by- 
combining  with  them  just  as  the  lime-water  combines 
with  the  lactic  acid  produced  by  the  bacteria  in  milk. 
The  antitoxins  may  remain  in  the  blood  for  a  long 
time  after  the  disease  disappears,  thus  making  it  diffi- 
cult or  impossible  for  the  disease  to  reappear.  This 
condition  is  known  as  immunity,  and  is  familiar  to 
us  in  the  cases  where  one  attack  protects  against 
another  for  a  long  period,  sometimes  for  a  lifetime 
(smallpox,  typhoid,  scarlet  fever,  etc.). 

The  principle  of  vaccination  depends  on  the  fact 
that  in  the  case  of  smallpox,  for  example,  germs  taken 
from  a  cow  with  "cowpox"  (a  similar  disease)  may 
be  introduced  into  the  human  system  and  produce  an 
exceedingly  mild  form  of  the  disease,  with  the  result 
that  the  body  produces  enough  antitoxins  to  give  it 
immunity  from  the  disease  for  a  long  period. 

In  some  cases  it  has  been  found  possible  to  obtain 
the  antitoxins  from  the  blood  of  an  immune  animal 
and,  by  injecting  them  into  another  animal  (or  the 
human  system),  confer  immunity  upon  it. 

In  addition  to  antitoxins,  there  are  antibacterial 
substances  (produced  in  much  the  same  way  as  the 
antitoxins)  which  act,  not  by  neutralizing  the  effect 
of  the  toxin,  but  by  destroying  or  checking  the 
bacteria. 

By  the  application  of  vaccination,  antitoxins,  etc., 
we  may  hope  ultimately  to  conquer  such  diseases  as 


380  UXPEBl.UKNTS    WITH   PLANTS 

typhoid,  lockjaw,  tuberculosis,  diphtheria,  pneumonia, 
cholera,  yellow  fever,  etc. 

Bacteria  which  live  in  living  plants  or  animals  are 
known  as  imrasitic^  while  those  which  live  in  decaying 
substances  are  called  saprophytic.  There  are  some  kinds 
which  live  in  both  ways;  such  are  capable  of  multiply- 
ing outside  the  living  body,  like  typhoid  bacilli,  and 
may  cause  infectious  diseases;  these  may  be  carried 
by  the  air,  by  streams,  etc.,  and  widely  distributed. 
Railway  trains  are  also  agents  of  distribution.  Flies 
are  especially  dangerous,  since  they  carry  disease  from 
the  filth  in  which  they  breed  directly  into  the  house. 
Tvy  the  experiment  of  letting  a  fly  crawl  over  sterilized 
gelatin  and  observe  the  colonies  of  bacteria  which 
spring  up  in  its  footprints.  Bacteria  which  cannot  live 
outside  the  body  can  cause  contagious  diseases  only 
(i.  e.  diseases  communicated  only  by  direct  contact 
with  the  diseased  person).  In  some  cases  such  bacteria 
(or  other  disease -producing  organisms)  can  be  trans- 
ferred by  mosquitoes  (malaria,  yellow  fever)  or  by 
fleas  (bubonic  plague).^ 

We  have  now  had  our  attention  called  to  several 
kinds  of  bacteria,  {a)  those  which  produce  decay  and 
putrefaction,  e.  g.,  those  which  flourish  in  infusions 
and  which  attack  and  destroy  the  potato  or 
gelatin;    {h)  those  which    cause   fermentation,  e.   g., 

1  See  an  article  by  Howard  in  the  Year-Book  of  the  U.  S.  Department  of 
Agriculture  for  1901. 


PLANTS    WHICH    'J  A  USE    DECAY  381 

those  which  change  milk-sugar  into  lactic  acid  and  so 
cause  the  souring  of  milk,  and  (c)  those  which  pro- 
duce disease.  It  must  not  be  supposed  that  these 
three  groups  can  be  sharply  separated,  for  all  bacteria 
cause  fermentation  and  decay  in  a  certain  sense.  Still, 
the  above  division  may  be  used  for  convenience;  let  us 
proceed  to  examine  the  first  two  classes  a  little  more 
in  detail. 

Decay  is  necessary  in  order  that  life  may  exist; 
hence  the  bacteria  of  decay  do  an  indispensable  work  in 
decomposing  the  dead  bodies  of  animals  and  plants  into 
such  substances  as  may  again  be  taken  up  by  plants  as 
food  and  so  eventually  made  available  to  animals. 

Hardly  is  an  animal  dead  before  the  bacteria  com- 
mence the  work  of  decomposition.  The  proteids,  fats, 
sugars,  etc.,  are  rapidly  split  up  into  simpler  com- 
pounds, with  the  result  that  finally  they  are  nearly  all 
converted  into  ammonia,  carbon  dioxide,  water  and 
hydrogen  sulphide  (a  gas  familiar  as  the  source  of  the 
characteristic  odor  of  rotten  eggs) .  In  the  decay  of 
plants  the  same  thing  occurs,  with  the  addition  that 
certain  special  bacteria  decompose  the  cellulose  and 
woody  fiber  into  carbon  dioxide  and  water  with  some 
evolution  of  hydrogen  and  marsh  gas. 

The  action  of  these  bacteria  is  further  illustrated 
in  the  decomposition  of  manure  and  sewage.  Two 
methods  of  purifying  sewage  by  bacterial  action  are 
in  extensive  use. 


382  EXPERIMENTS    WITH  PLANTS 

In  the  first,  the  sewage  is  left  for  six  to  twelve 
hours  in  a  shallow  open  basin  (contact  bed),  the 
bottom  of  which  is  covered  with  furnace  clinkers  or 
coke  (these  substances  help  to  purify  the  liquid) :  it  is 
then  conducted  into  a  similar  bed  for  six  to  twelve 
hours,  at  the  end  of  which  it  is  so  purified  that  it  may 
be  allowed  to  flow  into  a  neighboring  stream. 

In  the  second,  a  closed  underground  chamber 
(septic  tank)  with  a  vent-pipe  for  gases  is  employed: 
the  sewage  is  allowed  to  flow  slowly  through  it  in  a 
constant  stream;  on  emerging  from  this  it  is  greatly 
purified. 

This  helps  us  to  understand  the  self- purification  of 
rivers  and  streams.  For  example,  the  sewage  of 
Chicago  is  now  emptied  into  the  Illinois  river,  which, 
after  flowing  some  three  hundred  miles,  empties  into 
the  Mississippi  a  few  miles  above  the  point  from  which 
St.  Louis  takes  its  water  supply.  This  at  first  seems 
to  be  an  alarming  condition  of  things,  but  on  exami- 
nation it  has  been  found  that  this  water  has  no  more 
bacteria  than  neighboring  rivers  which  are  not  recipi- 
ents of  sewage.  The  purification  probably  depends 
largely  on  the  fact  that  the  bacteria  use  up  the  food 
supply  (i.  e.,  the  sewage  matter)  very  rapidly  and 
then  perish,  and,  further,  on  the  fact  that  they  slowly 
sink  to  the  bottom,  are  devoured  by  other  organisms, 
and  are  killed  by  sunlight  and  aeration. 

In  order  to  study  the  effect  of  aeration,  take  an 


PLANTS    WHICH    CAUSE    DECAY  383 

infusion  which  has  a  thick  film  of  bacteria  over  it  and 
pass  a  current  of  air  into  it  by  means  of  the  apparatus 
shown  in  Fig.  158.  Observe  the  rapidity  with  which 
the  water  becomes  clear. 

From  these  illustrations  we  may  gain  some  idea  of 
the  useful  work  done  by  the  bacteria,  which  have  been 
appropriately  called  the  scavengers  of  the  world. 

The  decomposition  of  manure  is  effected  by  bac- 
teria, the  most  important  product  from  a  practical 
standpoint  being  ammonia  gas.  The  ammonia  gas  is 
in  turn  acted  on  by  a  special  class  of  bacteria,  the 
nitrifying  bacteria.  Of  these  there  are  two  kinds, — 
the  nitrous  bacteria,  which  convert  ammonia  gas  into 
nitrous  acid  (and  nitrites) ;  and  the  nitric  bacteria, 
which  are  so  sensitive  to  ammonia  gas  that  they 
cannot  begin  to  work  till  it  has  all  disappeared,  but 
which  have  the  power  of  converting  nitrous  acid  (and 
nitrites)  into  nitric  acid  (and  nitrates),  in  which  form 
it  can  be  used  by  green  plants.  In  order  to  carry  on 
their  work  the  nitrifying  bacteria  must  have  plenty  of 
air.  Hence  it  would  seem  to  be  useful  to  allow  a 
circulation  of  air  in  the  manure -heap:  it  is  found, 
however,  that  there  are  denitrifying  bacteria  which 
convert  nitric  acid  into  free  nitrogen,  which  escapes 
into  the  air  ;  it  is  better,  therefore,  to  keep  the  heap 
closed  to  the  air  until  the  denitrifying  bacteria  have 
ceased  their  growth,  after  which  air  may  be  admitted 
to  stimulate  the  work  of  the  nitrifying  bacteria  (see 


384  EXPERIMENTS    WITH  PLANTS 

page  147) ;  these  bacteria,  it  should  be  said,  are  not 
confined  to  the  manure -heap  but  are  found  ahnost 
everywhere  in  soil  which  contains  organic  matter. ^ 

Occurring  in  soil  and  water,  along  with  the  bacteria 
just  mentioned,  are  found  the  nitrogen -fixing  bacteria, 
which  have  the  power  of  fixing  the  free  nitrogen  of  the 
air  and  converting  it  into  compounds  which  eventually 
become  available  to  the  plant.  Our  knowledge  of 
these  bacteria  is  as  yet  scanty,  but  several  of  them 
have  been  isolated  and  studied,  and  one  of  them  is 
offered  for  sale  as  an  almost  pure  culture  under  the 
name  of  "alinit"  (its  practical  value  is  still  in  dispute 
and  probably  depends  a  good  deal  on  local  conditions). 
Since  these  bacteria  need  abundance  of  air,  good 
tillage   is   important  in  promoting  their   activity. 

Another  kind  of  bacteria  which  also  possess  the 
power  of  fixing  free  nitrogen  and  making  it  available 
to  the  plant  inhabits  the  root  -  tubercles  of  certain 
plants  (principally  members  of  the  Pea  family) ,  which 
are  thus  able  to  draw  supplies  of  nitrogen  directly  from 
the  air.  On  this  account  they  are  of  inestimable  value 
as  green  manures  (see  page  149). 

It  is  found  that  if  these  plants  are  cultivated  in 
sterilized  soil  no  tubercles  appear;  furthermore,  such 
plants  begin  to  suffer  after  a  time  from  nitrogen 
hunger  ;    if  now  they  are  watered  with  soil  infusions 

1  See  an  article  in  the  Year-Book  of  the  U.  S.  Department  of  Agriculture 
for  1895  by  Wiley;  for  1902  by  Moore. 


PLANTS    WHICH    CAUSE    DECAY  385 

containing  the  tubercle  -  forming  bacteria,  they  soon 
form  tubercles  and  recover,  while  the  control  -  plants 
which  are  without  bacteria  do  not  recover.  It  is 
furthermore  found  that  if  the  roots  of  such  control- 
plants  are  pricked  with  a  needle  covered  with  the 
bacteria,  the  tubercles  develop  at  the  points  pricked. 

It  has  been  found  that  certain  kinds  of  Beans  fail  to 
grow  well  in  certain  localities  until  the  soil  there  is 
infected  with  the  proper  bacteria  by  bringing  soil  from 
another  locality  where  the  Beans  in  question  flourish. 
A  practically  pure  culture  of  one  species  of  tubercle 
bacteria  is  sold  under  the  name  "  Nitragin."  Its  use 
has  been  very  satisfactory  in  some  cases,  but  not  in 
others,  which  may  depend  on  the  fact  that  it  is  adapted 
to  certain  kinds  of  leguminous  plants,  but  not  to  others, 
and  perhaps  also  on  the  character  of  the  soil,  etc. 

In  order  to  preserve  foods,  the  bacteria  of  decay 
must  be  kept  in  check.  This  may  be  accom- 
plished by: 

{a)  Drying.— Bacteria  cannot  grow  in  dry  sub- 
stances. Their  growth  ceases,  as  a  rule,  when  the 
water- content  falls  below  25  per  cent.  Seeds  are  not 
subject  to  decay  as  long  as  they  are  dry.  Hay  and 
dried  fruits  are  further  illustrations.  Dried  meat  is 
commonly  smoked  as  well  as  dried;  the  smoke  has 
both  a  drying  and  a  germicidal  action. 

(&)  Preservatives. — The  most  important  of  these  is 
common    salt,    which   is    so   extensively   used   in   the 

Y 


386  EXPERIMENTS    WITH  PLANTS 

preservation  of  butter,  fish,  salt  pork,  corned  beef,  etc. 
Inasmuch  as  salt  does  not  kill  the  bacteria  (but  only 
checks  their  growth),  such  flesh  may  contain  disease- 
producing  bacteria,  and  be  unsafe  for  eating. 

Sugar  is  an  important  preservative.  In  some  dried 
fruits,  e.  g.,  raisins,  there  is  enough  water  to  permit 
the  bacteria  to  grow  were  it  not  for  the  sugar  which 
checks  them;  the  same  is  true  of  condensed  milk. 

In  addition  to  harmless  preservatives  such  as  salt, 
sugar  and  vinegar,  there  are  a  number  of  injurious  or 
poisonous  substances  used,  such  as  formalin,  salicylic 
acid  and  boracic  acid.  The  public  should  insist  that 
pure  food  laws  be  made  and  enforced,  to*  prevent  the 
use  of  such  preservatives. 

(c)  Heat. — The  important,  practical  application  of 
this  is  canning,  in  which  the  bacteria  are  destroyed  by 
heat,  and  the  cans  hermetically  sealed.  Tomatoes  and 
corn  are  difficult  to  can  properly  on  account  of  the 
presence  of  resistant  spores  which  are  not  killed  by  the 
heating,  and  which  cause  fermentation  inside  the  can ; 
the  cans  become  swollen  with  gas  so  that  the  head 
bulges  out;    such  cans  should  always  be  rejected. 

{d)  Cold. — The  use  of  refrigerators  by  families,  and 
the  construction  of  great  cold-storage  plants  in  cities, 
illustrates  the  importance  of  this  agent  of  preservation. 
It  should  be  remembered  that  cold  does  not  kill  many 
kinds  of  bacteria,  and  that  ice  may  be  a  source  of 
infection.    For  this  reason  it  is  always   better  to  cool 


I 


PLANTS    WHICH    CAUSE    DECAY  387 

water  by  putting  ice  around  the  vessel  containing  it 
rather  than  in  it. 

In  the  case  of  eggs,  bacteria  often  gain  entrance 
before  they  are  laid ;  if  this  is  not  the  case  they  can  be 
preserved  by  keeping  the  bacteria  out.  For  this  purpose 
the  pores  of  the  shell  are  filled  by  dipping  them  into 
water-glass  (vaseline  and  other  substances  have  been 
used;  they  are  also  packed  in  brine,  etc). 

Prominent  among  the  bacteria  of  fermentation  are, 
in  addition  to  the  lactic -acid  bacteria  of  milk,  the 
vinegar- making  bacteria.  In  order  to  study  these  bac- 
teria it  is  only  necessary  to  take  a  little  "mother" 
(which  is  a  gelatinous  mass  containing  the  bacteria) 
from  vinegar  and  place  it  in  a  little  hard  cider  or  a 
weak  solution  of  alcohol  (containing  not  more  than  6 
or  7  per  cent  alcohol)  neutralize  with  lime-water,  add 
enough  liquid  litmus  to  give  a  good  blue  color  and  allow 
it  to  stand  in  a  warm  place  (light  should  be  excluded) . 
If  the  liquid  be  poured  over  a  mass  of  excelsior  or 
shavings,  the  vinegar  is  formed  with  great  rapidity,  as 
shown  by  the  color  of  the  litmus. ^  The  reason  is  that 
in  this  case  the  bacteria  are  abundantly  supplied  with 
air,  which  is  essential  to  their  activity.  This  experi- 
ment may  be  conveniently  carried  out  in  a  covered 
wooden  pail  or  tub  filled  with  excelsior  (or  shavings) . 

In  recent  years  the  use  of  silage  has  become  very 
extensive.    Silage    is   made    by  filling  a  pit  or  other 

.  /.  Ordinary  litmus  paper  may  be  used  in  place  of  liquid  litmus. 


388  EXPERIMENTS    WITH  PLANTS 

air-tight  compartment  with  Corn  (or  some  other  plant) 
chopped  into  small  pieces.  It  is  packed  into  a  solid 
mass;  frequently  pressure  is  used  to  solidify  it.  The 
top  is  covered  (so  as  to  prevent  the  access  of  air).  A 
rapid  rise  in  temperature  occurs  (sometimes  going  as 
high  as  150°  F.) ;  after  a  few  days  the  mass  cools,  but 
the  evolution  of  heat  continues  to  a  lesser  degree  for 
several  weeks.  At  the  end  of  this  time  it  is  found  to 
be  somewhat  acid,  with  a  fine  aromatic  flavor  which 
causes  it  to  be  eagerly  eaten  by  cattle.  Silage  can  be 
made  just  as  well  in  small  pails  or  tubs  as  in  larger 
quantities,  and  the  phenomena  here  described  can  be 
observed  (only  the  rise  in  temperature  will  be  very 
small)  in  the  school -room. 

The  whole  process  looks  like  fermentation,  and  was 
until  recently  supposed  to  be  due  to  bacteria;  the 
latest  studies  indicate  that  bacteria  have  little  or  noth- 
ing to  do  with  it,  especially  in  the  early  stages,  ^here 
the  rise  in  temperature  seems  to  be  due  to  the  activity 
of  the  wounded  plant- cells.  In  this  respect  there  is  a 
close  agreement  between  animal-  and  vegetable- cells 
in  the  rise  of  temperature  (or  fever)  which  follows  a 
wound. 

The  fermentation  of  tobacco,  long  supposed  to  be 
due  to  bacteria,  has  lately  been  referred  to  the  self- 
activities  of  the  cells. of  the  leaf:  this  subject  is  still 
somewhat  in  dispute. 

The  "  sweating "  of  hay  is  in  all  probability  a  similar 


I 


PLANTS    WHICH    CAUSE    DECAY  389 

process  to  that  of  tobacco -curing,  but  how  far  it  is 
produced  by  bacteria  is  not  known. 

Another  class  of  plants,  very  different  from  the 
bacteria,  which  cause  fermentation  are  the  Yeasts. 
Eub  up  a  quarter  of  a  yeast -cake  in  water  to  make  a 
paste;  add  this  to  a  pint  of  water  in  which  a  table- 
spoonful  of  honey  or  sugar  has  been  dissolved.  Fill 
three  good- sized  bottles  half  full  of  the  (well -stirred) 
liquid,  and  stopper  them  by  simply  allowing  the  cork 
to  rest  in  the  neck  of  the  bottle  without  forcing  it 
down  into  it. 

Put  one  in  a  warm  place  in  the  dark,  one  in  a  cool 
place  (preferably  on  ice)  in  the  dark,  and  one  in  a 
warm  place  exposed  to  bright  light.  Observe  every  few 
hours,  noting  the  turbidity  of  the  liquid,  growth  of  the 
Yeast,  evolution  of  gas  bubbles,  change  in  taste,  etc. 

Repeat  the  experiments  shown  in  Figs.  30  and  31, 
using  Yeast  instead  of  seeds.  The  experiment  of  lower- 
ing a  lighted  match  into  a  bottle  in  which  Yeasts  are 
growing  may  also  be  tried:  if  it  goes  out  it  indicates 
the  presence  of  carbon  dioxide. 

Examine  under  the  microscope  a  little  of  the  yeast- 
cake  rubbed  up  in  water:  notice  the  appearance  of  the 
Yeast-cells:  add  a  little  iodine,  and  observe.  How  is 
the  yeast-cake  prepared? 

Take  some  of  the  sediment  from  the  bottom  of  the 
yeasu  culture  and  examine  under  the  microscope. 
Notice  the  appearance   of  the  Yeast- cell   (Fig.   213) 


390  JSXPEBIMENTS    WITH    PLANTS 

with  its  cell- wall, ^  and  protoplasm  filled  with  shining 
drops  or  granules.  The  mode  of  multiplication  can 
also  be  easily  made  out:  it  is  by  budding,  i.  e.,  an 
outgrowth  from  the  cell  becomes  cut  off,  and  forms  a 

new  cell.  The  cells  so  pro- 
duced often  hang  together 
in  chains  (Fig.  213). 

The     bubbles     of     gas 
which    rise   in    the    liquid 
are  practically  pure  carbon 
213.  Yeast-cells  budding.  dioxldc.    At  thc  samc  timc 

that  evolution  of  gas  goes  on,  alcohol  is  formed,  and 
the  sugar  disappears  (as  can  be  shown  by  tasting  the 
liquid).  Chemical  analysis  shows  that  the  sugar  is 
broken  up  by  the  action  of  the  Yeast  into  alcohol  and 
carbon  dioxide.  The  presence  of  alcohol  can  be  shown 
by  cautiously  heating  the  liquid  in  a  cup  until  enough 
vapor  forms  so  that  it  may  be  ignited  by  a  match: 
we  may  also  distil  off  the  alcohol  by  means  of  the 
apparatus  shown  in  Fig.  95. 

This  process  is  very  general  in  nature.  Nearly  all 
fruits  have  Yeasts  on  their  surfaces  which  cause  fer- 
mentation when  the  fruit  begins  to  decay,  converting 
the  sugar  present  into  alcohol  and  carbon  dioxide. 
Test  some  ripe  grapes  by  crushing  them,  covering  them 
with  water  and  allowing  them  to  stand  for  a  time; 
when  fermentation  occurs  examine  for  Yeasts. 

1  If  there  is  any  difficulty  in  seeing  the  cell-wall,  shrink  the  cells  by  the 
use  of  a  little  glycerine  or  strong  salt  solution. 


PLANTS    WHICH    CAUSE    DECAY  391 

In  the  maimfacture  of  beer,  etc.,  the  sugar  is  ob- 
tained by  allowing  the  grain  to  germinate  until  a  large 
part  of  its  starch  has  become  sugar  (see  page  169), 
then  killing  it  by  heat  and  extracting  the  sugar  by 
means  of  water;  the  Yeast  is  then  added.    In  addition 


214.    Black  Mould  of  'oread  (Rhizopiis),  showing  mycelium. 

to  the  useful  Yeasts,  there  are  others  which  impart  a 
disagreeable  taste  or  odor  to  the  product;  and  these 
must  be  carefully  excluded.  The  use  of  pure  cultures 
of  Yeasts  is  now  becoming  general:  they  are  obtained 
by  the  same  methods  as  pure  cultures  of  bacteria. 

Another  class  of  plants  which  resemble  the  bacteria 
in  causing  decay  are  the  Moulds.  A  very  common  one 
which  occurs  everywhere  on  decaying  fruit,  vegetables, 
bread,  etc.,  is  the  Black  Mould  of  bread  (known  as 
Mucor  stolonifer,  or  Bhizopus  nigricans) . 


392 


EXPERIMENTS    WITH  PLANTS 


Obtain  a  little  of  this  Mould  and  scatter  it  over  a  slice 
of  bread  which  is  kept  moist  in  a  granite -ware  pan 
covered  with  a  plate  of  glass  (Figs.  214,  216).  The 
first  thing  to  appear  is  an  abundant  growth  of  white, 
threadlike,  interlacing  filaments,  the  vegetative  part  of 
the  plant  (called  mycelium) .    This  is  shown  in  Fig.  217. 


215.     Same  beginning  to  show  spores  at  the  edges  of  the  bread. 

Presently  this  begins  to  darken  around  the  edges  of 
the  slice  (Figs.  215,  216).  When  we  examine  into  the 
cause  of  this,  we  find  numerous  little  black  bodies 
raised  on  slender  stalks  above  the  surface  of  the  bread 
(Fig.  217).  If  we  now  remove  a  portion  of  the  weft 
with  some  of  these  bodies  attached,  and  place  it  in  a 
drop  of  alcohol  on  a  slide,  and  place  a  cover -glass  on 
it,  and    add   a  drop   of  water  at  one   edge,  we  may 


PLANTS    WHICH    CAUSE    DECAY 


393 


examine  it  under  the  microscope   and   make   out  its 
structure  (Fig.  218). 

We  now  see  that  slender  threads  growing  over  the 
surface  of  the  bread  send  out  root -like  branches  at 
frequent  intervals,  and  that  from  these  points  stalks 


I 


More  advanced  stage  of  spore  formation. 


arise,  bearing  at  their  ends  round  bodies  (about  as  big 
as  the  head  of  a  very  small  pin)  which  are  at  first  white, 
and  later  turn  dark.  On  examining  with  the  high  power 
of  the  microscope,  we  see  that  each  of  these  bodies 
(Fig.  219)  has  a  chamber  (crescent- shaped  in  section) 
full  of  small  round  spores,  which  become  dark  as  they 
ripen  (crushing  by  pressing  on  the  cover- glass  with  a 
pencil -eraser  helps  to  bring  out  these  points). 

Try  to  find   the   youngest  stages   you  can  of  these 


394 


EXPEEIMENTS    WITH  PLANTS 


217.    Portion  of  the  mycelium,  showing  the  immature  spore-cases  (white)  and 
mature  ones  (black). 

spore -cases.  Why  do  they  appear  first  at  the  edges  of 
the  slice  (has  the  amount  of  moisture  anything  to  do 
with  it)  ?  Does  the  Mould  grow  better  in  the  light  or 
in  the  dark  ?  What  effect  has  temperature  on  its 
growth?  Does  it  produce  carbon  dioxide?  (Grow  some 
in  a  closed  jar  with  a  bottle  of  lime-water.) 


PLANTS     WHICH    CAUSE    DECAY 


395 


Sow  some  spores  in  a  hanging  drop,  as  shown  in 
Pig.  165,  and  observe  their  germination.  They  grow 
well  in  the  sweetened 
juice  of  stewed  apricots, 
in  water  in  which  hay 
has  been  boiled,  or  in 
sweetened  water.  Spread 
a  thin  layer  of 
nutrient  gela- 
tin (see  page 
369  ;  ordinary 
gelatin    sweet- 

anckrl      ^xrill      Ar\      218.     Black  Mould  of  bread,  showing  the  manner  in  which  the 
eneU      win      UO,  mycelium  sends  out  root-like  branches  at  short   intervals: 

or  even    a    little  ^^^^  t^^^Q  places  spring  long  stalks  bearing  spore-cases. 

clear  apple  or  other  fruit  jelly)  on  a  slide,  sow  the 
spores  in  it,  and  keep  the  slides  in  a  moist  atmosphere 
(for  this  purpose  they  may  simply 
be  laid  on  top  of  the  bread  culture 
in  the  pan  or  placed  in  a  special 
pan  on  a  support  to  keep  them 
from  contact  with  the  water  in  the 
bottom  of  the  pan).  We  may  re- 
move the  slides  from  time  to  time 
and  observe  the  development  of 
the  Mould  ;   since  they  are  injured 


219.  A  single  spore-ease  of    bv  exDOSurc  to  dry  air  it  is  better 

the  Black  Mould  of  bread,  J  t-  J 

(cr^^cem-'sSaped^S^sIc-    ^^  ^^^^^  ^  uumbcr  of  slldcs,  one  of 

tion)  in  which  the  spores 
(s)  are  contained. 


which  may  be  removed  each  day. 


396 


EXPERIMENTS     WITH    PLANTS 


The  spores  of  the  Mould  are  (like  the  spores  of  the 
bacteria)  resistant  cells  which  are  not  injured  by 
exposure  to  dry  air  and  are,  in  fact,  carried  about  by 
the  wind  so  as  to  scatter  the  Mould  everywhere.  When 
ripe  the  spore-case  bursts,  so  as  to  set  the  spores 
free. 

In  addition  to  these  spores  (called  asexual  spores) 
there   often   occur  larger  ones  (called   sexual   spores, 

or  zygospores,  because 
they  result  from  the  union 
of  two  branches),  which 
are  formed,  as  shown  in 
Fig.  220,  by  two  branches 
coming  together  and  fu- 
sing so  as  to  form  a  large, 
thick- walled  spore  of  a 
deep  black  color.    These 

220.     Formation  of  zygospores  of  the  black  SpOrCS      arC     larger,     mOre 
Mould  of  bread:  at  the  left  two  branches  .  . 

touching,  to  the  right  stages  in  the  fu-  rCSlStaut,        COUtam       mOl'C 
sion,  the  last  being  the  fully  formed  zygo- 

sp^^^-  nutriment   and  give  rise 

on  germination  to  a  more  vigorous  growth  than  the 
ordinary  asexual  spores. 

Another  very  common  Mould  is  the  Green  Mould 
(Penicillium)  of  cheese,  bread,  jellies,  etc.  In  this 
Mould  the  spores  are  in  long  chains  at  the  end  of  the 
stalk  (Pig.  221),  and  are  not  enclosed  in  a  spore-case, 
as  in  the  Black  Mould. 

What  effect  do  these  Moulds  have  on  the  substances 


PLANTS    WHICH    CAUSE    DECAY 


397 


on  which  they  grow  ?    Can  foods  be  protected  against 
them  in  the  same  way  as  against  bacteria  ?  ^ 

An  immense  amount  of  damage,  amounting  in  the 
United  States  alone  to  a  great  many 
minions  of  dollars  each  year,  is  done 
to  crops  by  the  Smuts,  Rusts  and 
Mildews.  For  this  and  other  reasons 
it  is  worth  while  to  devote  some 
study  to  these  plants,  in  order  that 
we  may  more  clearly  understand  their 
mode  of  life  and  the  best  remedies 
against  them. 

The  common  Corn-smut  begins  to 
appear  in  the  leaves  when  the  plant 
is   three   or  four  feet  high,  forming 

•        T         1  2^^-  Grreen  Mould  of  cheese, 

small   white   spots   raised  above  the       etc.,  showing  the  man- 

■"•  ner  in  which  the  spores 

surface  of  the  leaf  and  somewhat  ^*^  ^""^  ^°''''®- 
wrinkled  (frequently  surrounded  by  a  reddish  dis- 
coloration of  the  leaf).  Later  on  they  turn  black 
(or  disappear  altogether) .  The  Smut  appears  on 
the  stalk,  inside  the  sheathing  base  of  the  leaf,  near 
the  joint  or  node.  It  also  appears  in  the  form  of 
pustules  scattered  through  the  male  flowers  or  tas- 
sel ;  it  also  appears  on  the  ears,  covering  them 
partially  or  completely,  forming  white  masses  with  a 
peculiar   soft,    silvery   luster ;    later   these   burst    and 

^  A  very  good  method  of  sealing  jellies  is  to  pour  melted  paraffin  on  top  : 
the  heat  kills  the  Moulds  and  bacteria  while  the  paraffin  seals  the  tumbler  her- 
metically. 


398  EXPERIMENTS    WITH  PLANTS 

discharge  a  perfect  cloud  of  black  spores.  If  we 
investigate  these  masses  before  they  have  grown  to 
the  size  of  a  pea  we  find  a  mass  of  mycelium,  similar, 
in  a  general  way,  to  that  of  the  Bread  Mould;  later  on 
this  mycelium  forms  spores  by  breaking  up  into  its 
constituent  cells,  which  separate  from  each  other,  each 
cell  becoming  a  spore.  The  spores  are  scattered  by  the 
wind  and  germinate  in  the  soil  or  wherever  they  can 
find  moisture  and  suitable  food.  Germination  may 
take  place  at  once  or  may  occur  the  following  season. 
In  order  to  see  the  germination  of  the  spores,  we  may 
cultivate  them  in  a  hanging  drop  of  steril- 
ized dung  liquor,  sterilized  plum  juice  (made 
by  stewing  prunes  in  water  and  just  neutral- 
izing the  acid  by  adding  ammonia  water), 
Pasteur's  solution^  with  sugar  or  in  modified 
Cohn's  solution.- 

The  spore  first  puts  out  a  germ- tube  (Fig. 
222) ;  when  this  has  become  several  cells 
long,  elongated  spores  make  their  appearance 
(Fig.  223,  c) ;  these  are  called  conidia,  .  They  develop 
much  more  abundantly  in  contact  with  air  (i.  e.,  on  the 
surface  of  the  liquid).    It  is  the  conidia  which  infect 

■  -iTliis  can  be  made  np  by  a  druggist  as  follows:  Monobasic -potassium 
phosphate,  20  partsj  tribasic  calcium  phosphate,  2  parts;  magnesium  sulphate, 
2  parts  ;  ammonium  tartrate,  100  parts;  cane-sugar,  1,500  parts;  water,  8,576 
parts. 

2  This  may  be  made  up  by  a  druggist  as  follows  :  Distilled  water,  42.385 
grams  ;  cane-sugar,  7  grams  ;  ammonium  tartrate,  .250  grams  ;  potassium 
phosphate,  .125  grams;  magnesium  sulphate,  .125  grams;  calcium  phosphate, 
.125  grams. 


PLANTS    WEIGH    CAUSE    DECAY 


399 


c— 


the  Corn  plant.  Borne  by  the  wind,  they  settle  upon 
the  plant  and  penetrate  it  wherever  the  tissues  are 
sufficiently  tender,  i.  e.,  at  the 
terminal  buds  and  at  the  base  of 
the  leaves,  inside  the  sheath.  Any- 
thing which  tends  to  make  the 
Corn  tender  and  succulent  (e.  g., 
rich  land  and  abundant  water) 
favors  infection;  moisture  in  the 
air  also  helps  to  preserve  the  vital- 
ity of  the  conidia,  which  are  in- 
jured or  killed  outright  by  drying 
up.  The  conidia  germinate  by  send- 
ing out  a  germ- tube,  which  pene-  223.  spore  of  com-smut  pro- 
trates  into  the  tissues  of  the  Corn  ^^'^^ 

plant,  where  the  mycelium  rapidly  spreads  to  all  parts. 
(When  food  is  not  abundant  they  frequently  unite  in 
pairs  before  sending  out  the  germ -tube.) 

The  best  method  of  infecting  the  Corn  is  as  follows : 
Grow  the  spores  in  one  of  the  above  solutions  (pref- 
erably plum  juice  or  Pasteur's  solution  with  sugar), 
until  examination  shows  the  formation  of  abundant 
conidia.  With  a  medicine -dropper  place  a  few  drops 
of  the  liquid  {a)  on  some  Corn  seedlings  (with  leaves 
about  half  an  inch  long)  grown  between  folds  of  moist 
cloth  or  blotting-paper;  leave  them  for  at  least  twenty- 
four  hours  more  in  the  blotting-paper,  then  transplant 
several  of  them  to  pots  of  sterilized  soil  (leaving  the 


400  EXPEBIMENTS    WITH  PLANTS 

others  still  iii  the  blotting-paper).  Have  a  number  of 
uninfected  plants  as  a  control.  If  growing  Corn  is 
available,  (6)  place  a  few  drops  in  a  young  ear  by 
gently  opening  the  end  of  the  ear  and  forcing  the 
pipette  down  into  the  center.  Results  from  {a)  should 
be  apparent  in  about  two  weeks.  If  no  result  is 
obtained,  repeat  the  experiment. 

The  yearly  loss  from  Corn- smut  in  the  United 
States  alone  is  estimated  at  over  $2,000,000.  The  best 
remedy  is  to  go  through  the  fields  once  or  twice  during 
the  growing  season  and  again  when  the  Corn  is  ripen- 
ing, collecting  all  the  smutted  portions  each  time  and 
burning  them.  Formerly  the  seed  was  treated  with 
bluestone,  but  this  is  of  no  value,  because  the  infection 
occurs  after  germination. 

The  Smuts  of  Grrain^  (i.  e.,  the  Black  Smuts  of 
Wheat,  Oats,  Barley  and  Rye  and  the  Stinking  Smut 
of  Wheat)  do  not  spread  from  plant  to  plant,  like  the 
Corn- smut;  infection  takes  place  only  when  the  spores 
come  in  contact  with  the  seed;  for  this  reason  the 
attacks  of  these  Smuts  may  be  prevented  by  treating 
the  seeds  with  a  germicide.  For  this  purpose  blue- 
stone  (copper  sulphate  or  blue  vitriol)  is  used  at  the 
rate  of  a  pound  (or  more)  to  a  gallon:  the  seeds  are 
dipped  into  this  long  enough  to  get  thoroughly  wetted 
(wheat  for  a  few   minutes,  oats   and    barley,   on  ac- 

1  See  an  article  by  Swingle  in  the  Year  -  Book  of  the  United  States  Depart- 
ment of  Agriculture  for  1894;  for  1896  by  Carleton, 


I 


PLANTS    WHICH    CAUSE    DECAY  401 

count  of  their  hulls,  from  eighteen  to  forty  hours),  and 
then  dried  (this  is  hastened  by  dusting  them  with 
plaster  or  slaked  lime)  before  sowing.  Very  favorable 
results  have  been  obtained  with  oats  by  dipping  for 
ten  minutes  in  formalin  (one  pint  of  formalin  in  thirty- 
six  gallons  of  water).  Other  precautions,  in  addition 
to  the  use  of  germicides,  are  to  grow  some-  other  crop 
besides  Grain  until  the  spores  in  the  soil  are  dead  (two 
or  three  years) ;  to  keep  cattle  and  manure  off  the 
land  where  there  is  any  danger  of  carrying  the  spores, 
and  to  disinfect  the  barn,  bin,  thresher,  etc.  The  loss 
in  the  United  States  from  Oat- smut  alone  is  estimated 
at  over  $18,000,000. 

If  these  Smuts  occur  in  your  vicinity,  it  will  be 
very  easy  to  watch  the  germination  of  the  spores  in 
hanging  drop  cultures,  and  also  to  make  experiments 
to  determine  the  relative  value  of  germicides  and 
whether  they  impair  the  germination  of  the  seed.  If 
clean  seed  is  obtainable,  infections  may  be  made. 

The  Black  Stem  Eust  of  Grain  has  a  very  different 
appearance  and  mode  of  life  from  the  Smuts  of  Grain. 
Instead  of  being  confined  to  the  flowers,  it  appears  on 
the  whole  plant,  principally  on  the  stalks  and  leaves, 
where  it  forms  elongated  black  ("black  rust")  or  red 
("red  rust")  pustules.  The  red  pustules  contain  one- 
celled  spores  (called  summer  spores  or  uredorspores) , 
as  is  shown  in  Fig.  224;  the  black  pustules  contain 
two -celled  spores   (called   autumn   spores    or  teleuto- 

z 


402 


EXPERIMENTS    WITH  PLANTS 


spores),  as  shown  in  Fig.  225.    These  two  forms  of 
spores  are  developed  from  the  same  mycelium,  the  one 


224,  Summer  spores,  or  uredo- 
spores  (red  rust  stage),  of  the 
Black  Stem  Rust  of  Wheat. 


225.  Autumn  spores,  or  teleuto- 
spores  (black  rust  stage) ,  of  the 
Black  Stem  Rust  of  Wheat. 


(uredospores)  earlier,  the  other  (teleutospores) ,  later 
in  the  season.  The  uredospores  germinate  during  the 
summer;  they  send  out  germ-tubes  which  enter  the 
stomata  of  the  leaf  (Fig.  226).    The  teleutospores  rest 

during  the  winter;  in  the 
spring  they  germinate, 
producing  conidia  (Fig. 
227,  c) ,  which  are  borne  by 
the  wind  to  the  leaves  of 
the  Barberry  plant;  here 
they  germinate,  penetrat- 

226.  Summer  spores  of  the  Black  Stem  Rust  *  ^  fVio  Incif  Kat  TvioQna  r^f 
of  Wheat,  germinating  on  a  Wheat  leaf  ^^&  ^^'^^  ^^"^^  ^V  UieaUb  OL 
and  sending  the  germ  tubes  through  the  ,     ,  in 

stomata.  a  gcrm-tube  and  forming 


PLANTS    WHICH    CAUSE    DEC4.T 


403 


a  mycelium  which  spreads  rapidly  through  the  leaf  and 
finally  forms  spores  known  as  cluster- cup  spores  (or 
aecidiospores) .  These  spores,  as  their  name 
implies,  are  arranged  in  clusters  in  cup- 
like cavities  of  the  leaf  (Fig.  228),  which 
are  produced  by  their  growth.  On  exam- 
ining thin  sections  of  the  leaf  carefully,  we 
see  that  the  cluster- cup  spores  are  in  long 
chains  borne  on  short  stalks  (Fig.  229). 
On  the  upper  surface  of  the  leaf  occur 
smaller  cavities  filled  with  smaller  slender 
spore- bearing  stalks;  their  function  is  not 
understood.  We  see,  then,  that  the  Black 
Stem  Rust-  of  the  Wheat  occurs  in  three 
different  forms,  at  different  times  of  the 
year — the  uredospores  in  the  summer,  the 
teleutospores  in  the  autumn,  and  the  clus- 
ter-cup spores  on  Barberry  in  spring.    Formerly,  when 

it  was  not  known  that 
these  were  all  forms  of 
the  same  fungus,  they 
were  described  as  sepa- 
rate genera.  The  discov- 
ery that  the  Barberry  had 
something  to  do  with  the 
Rust  on  Wheat  was  first 

,    Section  of   Barberry  leaf,  showing  the     made     by    praCtlcal    farm- 
cluster-eiip  stage  of  Black  Stem  Rust  ol  •,  ,  n       i  i      j 

Wheat.  ers,    who    observed    that 


227. 

Autumn  spores 
of  the  Black 
Stem  Rust  of 
Wheat  poduc- 
ingconidialc). 


404 


EXPERIMENTS    WITH   PLANTS 


Wheat  was  more  affected  with  Rust  when  it  stood  on 
the  leeward  side  of  a  Barberry  bush;  it  was  accord- 
ingly decreed  by  the  Massachusetts  Barberry  Law  of 
1755   that  the  Barberry  bushes   should  be  destroyed. 

The  matter  was 
Ci5:>^^,_^    afterward  taken 

7n^;^^a up  by  botanists, 

who  traced  the 
connection  care- 
fully and  came 
to  the  conclu- 
sion that  the 
cluster -cup  was 
a  necessary 
stage  in  the  life- 
history    of    the 

229.    Cluster-cup  (aecidium)  of  Black  Stem  Rust  ot  Wheat,      n  k     t  rv* 

fungus.  A  diffi- 
culty arose  in  the  fact  that  the  Eust  prospers  even 
when  there  are  no  Barberry  bushes,  and  it  is  now 
known  that,  in  some  cases  at  least  (e.  g.,  in  Australia) , 
the  uredospores  can  live  through  the  winter  and  infect 
the  Wheat  again  in  the  spring.  It  is  supposed,  how- 
ever, that  the  teleutospores  cannot  infect  Wheat,  but 
only  Barberry. 

The  uredospores  of  the  Black  Stem  Rust  of  the 
Wheat  readily  infect  Barley,  and  vice  versa;  but  it 
seems  highly  probable  that  they  cannot  infect  Oats 
(nor  vice  versa) .    The  Black  Stem  Rust  of  Oats  seems 


PLANTS    WHICH    CAUSE    DECAY  405 

to  be  a  distiDct  form,  though  it  in  every  respect  closely 
resembles  that  of  the  Wheat,  and  passes  its  cluster- 
cup  stage  on  the  Barberry.  The  same  is  probably  true 
of  the  Black  Stem  Rust  of  the  Rye:  it  does  not  appear 
to  affect  any  other  Grain. 

The  Orange  Leaf  Rust  of  the  Wheat  is  very  similar 
in  appearance  to  the  Black  Stem  Rust;  its  cluster- cup 
stage  is  passed  on  Anchusa  and  Echium;  the  uredo 
lives  over  the  winter  in  the  United  States.  The  Orange 
Leaf  Rust  of  the  Rye  appears  to  be  distinct  from  that 
of  Wheat:  its  uredo  lives  over  the  winter  in  the 
southern  states. 

The  Crown  Rust  of  Oats  is  found  only  on  Oats.  It 
resembles  the  Orange  Leaf  Rust  of  Wheat.  Its  cluster- 
cup  stages  are  passed  on  Rhamnus. 

The  method  of  observing  the  germination  of  the 
cluster -cup  spores  or  the  uredospores  is  simply  to 
place  perfectly  fresh  spores  in  a  hanging  drop  of  water. 
The  teleutospores  are  to  be  treated  in  the  same  manner, 
only  they  must  be  preserved  during  the  winter,  for  they 
will  germinate  only  in  the  spring.  These  germination 
experiments  may  not  always  succeed,  but  they  are 
worth  trying. 

In  order  to  make  infections  with  uredospores,  it  is 
only  necessary  to  grow  some  Wheat  in  pots  during  the 
summer;  and  when  the  leaves  are  three  or  four  inches 
long,  bring  in  a  fresh  leaf  of  Wheat  which  is  well  covered 
with  uredospores,  and  tie  two  of  the  growing  Wheat 


406  EXPEBIMENTS    WITH   PLANTS 

leaves  together,  with  the  infected  leaf  between  them, 
in  such  a  way  that  there  will  be  a  close  contact  all 
along  the  leaf:  this  will  ensui'e  the  uredo- spores  reach- 
ing  the  growing  leaves,  and  will  prevent  them  from 
drying  up.  The  moister  the  air  is  kept,  the  better;  it 
may  be  well,  therefore,  to  cover  the  plants  with  a 
paper  bag  (or,  better  still,  with  a  bell-jar  if  available). 

The  common  Hollyhock  Rust  (found  everywhere  on 
Hollyhocks,  the  Round -leaved  Mallow  and  other  Mal- 
lows) is  an  example  of  a  Rust  which  passes  through 
its  entire  life- history  on  one  kind  of  plant,  thus  con- 
trasting with  the  Rusts  of  Grain:  it  produces  teleudo- 
spores  only;  they  germinate  readily  in  water  and  may 
be  used  for  infection  experiments  (either  by  putting  a 
drop  of  water  containing  the  spores  between  two  leaves 
tied  together  or  by  using  the  infected  leaf  in  the 
manner  described  above) . 

The  yearly  loss  from  Grain  Rusts  in  the  United 
States  is  estimated  at  considerably  more  than  $18,- 
000,000. 

As  an  example  of  a  Mildew  we  may  study  the  com- 
mon Mildew  of  the  Lilac.  The  mycelium  appears  on 
the  surface  of  the  leaf  as  a  whitish  covering  (scrape 
off  a  little  of  this,  mount  it  in  a  drop  of  weak  alcohol 
and  examine  imder  the  microscope).  After  a  time 
black  specks,  visible  to  the  naked  eye,  appear  here  and 
there  on  the  mycelium.  Remove  some  of  them  and  ex- 
amine under  the  microscope :  they  have  the  appearance 


PLANTS    WHICH    CAUSE    DECAY  407 

shown  in  Fig.  230.  The  long,  branching  appendages 
of  the  rounded  black  bodies  are  very  characteristic. 
Press  on  the  cover-glass  with  a  rubber  pencil -eraser 
until  some  of  the  black  bodies  are  crushed;  we  may 
then  see  the  spore- sacs,  containing  four  or  more 
spores. 

Mildews  are  very  common  on  both  wild  and  culti- 
vated  plants 
and  do  a  large 
amount  of  dam- 
age. They  do 
not  penetrate  to 
any  great  extent 
into  the  leaf  but 

absorb  nUtri-  930.  Penthecmm  of  the  common  Mildew  of  the  Lilac;  spore- 
TTIPnt     bv    mParm        sacs  (asci)  issuing  from  an  opening  produce!  by  crushing. 

of  short  sucking  organs  which  penetrate  into  the 
epidermal  cells. 

Most  of  the  loss  from  plant  diseases  is  preventable 
by  simple  measures;   among  these  are  the  following i^ 

(1)  Spraying  with  chemicals  (Bordeaux  mixture, 
sulphur,  etc.)  which  do  not  injure  the  plant. 

(2)  Destruction  of  diseased  plants  or  portions  of 
them  by  burning;   this  of  course  destroys  the  spores. 

1  Consult  Ward:  "Disease  in  Plants";  Lodeman:  "The  Spraying  of 
Plants";  Ward:  "Timber  and  Some  of  its  Diseases";  Massee:  "Text-book  of 
Plant  Diseases";  also  articles  in  the  Year-Book  of  the  U.  S.  Department  of 
Agriculture  for  1895  by  Waite  and  by  Galloway  and  Woods;  for  1896  by  de 
Schweinitz  and  by  Howard;   for  1899  by  Galloway;   for  1900  by  von  Schrenk. 


408  EXPERIMENTS    WITH  PLANTS 

Weeds,  volunteer  Grain,  etc.,  along  roadsides  and  in 
fence  corners  may  harbor  the  disease,  and  hence  should 
be  kept  down  as  much  as  possible. 

(3)  Rotation  of  crops  in  the  case  of  diseases  which 
can  live  in  the  soil;  this  allows  them  to  die  out  in  the 
interval  between  crops.  Plants  with  such  diseases 
should  be  burned  rather  than  plowed  under. 

(4)  Disinfection  of   seed,  seed   bins,  thresher,  etc. 

(5)  Careful  attention  to  wounds,  cuts  made  in 
pruning,  etc.  These  should  be  repeatedly  painted  with 
tar  to  prevent  the  entrance  of  disease. 

Among  the  books  which  may  be  consulted  on  the  subject  of  the  chapter 
are:  Conn:  "Story  of  Germ  Life."  "Bacteria,  Yeast  and  Molds  in  the  Home," 
"Agricultural  Bacteriology;"  Newman:  "Bacteria," 


CHAPTER    X^ 
MAKING  NEW  KINDS  OF  PLANTS  2 

It  was  not  long  ago  that  the  finest  Tomatoes  were 
so  small,  tasteless  and  full  of  seeds  as  to  be  utterly 
unfit  to  eat;  at  that  time  they  were  called  "Love- 
apples"  and  were  grown  merely  as  curiosities.  The 
splendid  varieties  of  the  present  have  all  been  made  in 
a  generation. 

All  our  cultivated  fruits  have  been  similarly  im- 
proved. How  this  is  done  is  well  illustrated  in  the 
work  of  Mr.  Luther  Burbank  on  Plums.  He  began  by 
carefully  studying  the  various  kinds  of  Plums  obtain- 
able from  this  and  other  countries,  with  a  view  to 
finding  out  their  individual  peculiarities  and  possi- 
bilities of  improvement.  Then  he  crossed  American, 
Japanese  and  European  kinds  together,  and  from  the 
resulting  mixture  selected  the  best  for  further  experi- 
ments, destroying   the    rest.     The    results    have    been 

1  Indispensable  for  reading  in  connection  with  this  chapter  is  "Plant 
Breeding,"  by  L.  H.  Bailey.  Both  the  second  edition  (1902)  and  the  third 
edition  (1904)  should  be  at  hand,  since  the  former  contains  an  interesting 
chapter  omitted  from  the  last  edition.      Also  de  Vries:  "Plant  Breeding," 

2  Of  the  illustrations  in  this  chapter  I  am  indebted  to  Mr.  Luther  Burbank 
for  Figs.  231  to  236  and  240  to  245,  and  to  Professor  Hugo  de  Vries  for 
Figs.   247  to  252. 

(409) 


410  EXPERIMENTS    WITH    PLANTS 

extraordinary:    they   may   be    briefly  summed    up    as 
follows : 

1.  Every  possible  variety  of  coloring  of  skin  and 
flesh  has  been  obtained,  from  a  pure  golden  yellow  to 
deepest  blood -red.  Mottled  and  variegated  forms 
have  appeared  in  abundance. 

2.  The  shapes  vary  as  much  as  the  colors.  The 
■'Apple  Plum"  has  the  size,  shape  and  appearance 
of  an  apple:  others  are  like  an  inverted  pear,  while 
all  the  intermediate  shapes  are  represented. 

3.  The  new  flavors  and  aromas  defy  classification. 
While  the  Bartlett  Plum  tastes  exactly  like  the  Bartlett 
Pear,  others  suggest  a  banana,  and  all  degrees  of 
sweetness  and  acidity  are  found.  Some  have  the 
aroma  of  pineapples,  others  of  apples,  and  of  certain 
kinds  but  a  few  are  needed  to  fill  a  whole  room  with 
fragrance. 

4.  The  sizes  have  been  increased  up  to  three  inches 
long  and  two  and  one -half  in  diameter.  That  the 
hybrid  may  sometimes  exceed  either  of  the  parents 
in  size  is  well  shown  in  Fig.  231.  The  parents  are 
an  American  Plum  (Primus  Americana)  shown  on  the 
right,  and  a  Japanese  Plum  {Primus  triflora)  ^  shown 
on  the  left.  Among  the  hybrids  which  appeared  in 
the  first  generation  of  this  cross,  before  any  selection 
had  taken  place,  was  the  one  shown  in  the  center 
of  the  figure.  The  Giant  Prune,  over  two  and  one- 
half  inches  long,  is  another  very  interesting  illustration 


MAKING    NhJW   KINDS    OF   PLANTS 


411 


of  this  point;  it  is  a  cross  between  the  French  Prune 
(shown  in  Fig.  1236)  and  the  Pond  Plum  (a  European 
Plum  about  one  and  three-quarter  inches  in  length), 


a 


231.  Increased  size  iu  Plums  due  to  hybridization  (without  selection).  Japanese 
parent  on  the  left,  American  on  the  right,  hybrid  iu  the  center.  Two-thirds 
natural  size. 

and  was  brought  to  its  present  huge  size  by  con- 
tinued selection:  it  therefore  owes  its  size  to  crossing 
plus  selection.  Another  offspring  of  the  French 
Prune,  called  the  Sugar  Prune  (Fig.  232),  is  not 
only  much  larger  but  ripens  a  month  earlier  and 
is  even  sweeter  than  the  parent,  running  as  high  as 
about  24  per  cent  sugar,  or  practically  one -fourth 
of  the  total  weight  of  the  fresh  fruit.  This  was 
obtained  simply  by  selection,  no  crossing  having 
been  done.  These  three 
instances  illustrate  very 
well  the  different  ways  of 
securing  increased  size. 

rr      -r%                n        •                   •  '->^--     Increased  size  in  Plums  due  entirely  to 

0.    l3y  producing  vane-  selection  (without  crossing).   French  Prune 

.  .               1   •    1         •                                 i  1  (dried)  on  the  left;  Sugar  Prune  (dried)  on 

ties   which  ripen  a  month  the  right.  Two-thirUs  natural  size. 


412  EXPERIMENTS     WITH   PLANTS 

before  the  earliest  of  the  old  varieties,  and,  on  the 
other  hand,  varieties  whioh  last  until  December,  the 
Plum  season  has  been  greatly  prolonged.  The  impor- 
tance of  early  and  late  varieties  is  very  great,  since 
they  enter  the  market  without  competition  in  their 
particular  line. 

6.  Some  varieties  have  been  produced  which  seem 
to  be  unaffected  by  frost.  Even  though  the  petals  and 
young  leaves  are  frozen  and  killed,  the  stamens  and 
pistils  go  on  performing  their  functions  and  the  trees 
bear  a  full  crop  of  fruit.  Other  varieties  have  been 
obtained  which  are  enormously  productive  even  where 
the  old  varieties  fail.  Many  of  these  begin  to  bear 
abundantly  the  third  year  from  the  seed  when  grafted 
upon  trees  of  ordinary  size;  others  have  been  bred 
to  stand  shipping  for  long  distance.  Some  kinds 
have  been  secured  which  remain  on  the  tree  from  six 
to  nine  weeks  in  hot  weather  without  deterioration, 
thus  possessing  a  great  advantage  over  many  of  the 
older  varieties  which  must  be  picked  as  soon  as  ripe. 

Some  of  these  new  Plums  are  accommodated  to 
climates  and  conditions  where  the  Plum  has  hitherto 
proved  a  failure.  A  notable  instance  of  this  is  the 
Improved  Beach  Plum  (Fig.  233),  obtained  by  crossing 
the  Beach  Plum  (Prunus  maritima)  with  an  American 
Plum  {Primus  Americana).  The  Beach  Plum  is  a  wild 
species  growing  along  the  coast  as  a  low,  spreading 
shrub,  not  more  than  three  or  four  feet  high,  with  a 


MAKING    NEW    KINDS    OF    PLANTS 


413 


very  dull -colored,  small,  bitter  fruit  (see  Fig.  233), 
utterly  worthless  except  for  preserving.  It  has  the 
advantage  of  growing  in  all  situations,  thriving  in  dry 
sand  or  in  the  soggy  soil  of  swamps,  indifferent  to 
cold  and  frost  and  wonderfully  prolific. 

By  crossing   and    selection,   the    good   qualities  of 
both  parents   have   been   retained   and    the   bad    ones 


233.    Improved  Beach  Plum  in  the  tenter.     The  parents  are:  Beach  Plum  on  the  right, 
an  American  Plum  on  the  left.    Natural  size. 


eliminated.  The  Improved  Beach  Plum,  as  it  is  called, 
bears  so  abundantly  that  the  fruit  almost  conceals  the 
wood,  as  may  be  readily  seen  from  the  photograph 
(Fig.  234) ,  which  represents  a  branch  three  and  a  half 
feet  long.  The  fruit  is  shown  full  size  in  Fig.  233. 
It  is  of  a  deep  purple  color,  with  white  dots,  with  deep 
yellow  flesh  and  a  stone  not  larger  than  a  cherry -pit. 
It  is  a  delicious  plum  of  unusually  fine  flavor,  without 
a  trace  of  the  bitter  taste  of  the  Beach  Plum.  It  is 
indifferent  to  frost,  and  grows  and  bears  under  the 
most  trying  conditions  of  soil  and   climate,  and  will 


234.    A  branch  of  the  Improved  Beach  Plum.    (The  fruit  is  shown 
natural  size,  in  Fig.  233.)     Less  than  one-eighth  natural  size. 


MAKING    NEW   KINDS    OF    PLANTS  415 

produce  abundantly  where  Plum   culture  has   hitherto 
been  impossible. 

An  interesting  departure  has  been  made  by  crossing 
Plums  with  other  fruits.  A  cross  between  the  Plum 
and  an  evergreen  Cherry  has  been  made  which 
promises  most  striking  results.  A  still  more  re- 
markable cross  is  between  the  Plum  and  the  Apricot, 
which  Mr.  Burbank  succeeded  in  making,  after  making 
many  trials,  and  which  he  has  called  the 
Plumcot  (Fig.  235).  This  resembles  an 
apricot  but  is  more  highly  colored,  with 
very  fine  silky  down:  the  pit  some- 
times resembles  that  of  a  plum,  some- 
times  that  of  an    apricot:     the  leaf  is  035.    The  pinmcot 

,  t/tj  ill  pji  cross     between     the 

mtermediate  between  the  leaves  01  the      pium  and  the  Apri- 
cot.   One  -  half  nat- 

parents.     The    flavors   are  unique   and      ^»"ai  size. 
varied  and,  taken  all  together,  it   is  a  most  remark- 
able and  delicious  fruit. 

Not  content  with  these  achievements,  he  conceived 
the  idea  of  producing  a  Stoneless  Plum  and  Prune. 
Beginning  with  a  small,  unproductive  variety,  with 
fruit  no  larger  than  a  cherry,  but  with  a  stone  w^hich 
only  partially  covered  the  kernel,  he  crossed  it  care- 
fully with  the  French  Prune  and  selected  the  progeny 
until  a  variety  of  new  Plums  were  obtained,  all  of 
good  size,  good  flavors  and  fine  appearance,  and 
all  destitute  of  stones.  In  the  center  is  no  stone, 
but   in   its    place  a  cavity  within  which  lies   a  more 


416 


JSXPEBIMENTS    WITH  PLAN'lti 


or  less  well -developed  seed.  Some  of  the  seeds  are 
normal  in  size  and  shape,  others  more  or  less  de- 
formed and  abortive,  while  in  a  certain  percentage 
seed   and    stone    are    both   absent.     Fie:.    236   shows, 


236.  The  Stoneless  Plum,  lowet  row;  and  parents,  upper  row.  At  the  right  in  the 
lower  row  the  StoneIes.s  Plum,  external  appearance;  in  the  middle  the  fruit  cut  open 
showing  a  normal  seed  with  a  cavity  where  the  stone  would  ordinarily  be;  at  the 
left,  another  frnit  containing  neither  stone  nor  seed,  the  latter  being  represented 
by  a  shriveled  remnant.  In  the  upper  row  the  parents:  at  the  right  the  French 
Prune;  at  the  left  the  Prunier  sans  Noyau.     All  natural  size. 

in  the  middle  of  the  lower  row,  one  of  these  prunes 
cut  across;  in  this  a  well -developed  seed  is  present: 
on  the  left  is  shown  another  in  which  nothing  remains 
of  the  seed  save  an  abortive  remnant.  While  Mr, 
Burbank  believes   it    perfectly  possible  to   breed   out 


MAKING    NEW    KINDS    OF    PLANTS  417 

the  seed  altogether,  he  does  not  consider  it  desirable 
to  do  so,  for  the  reason  that  the  seed  adds  flavor  to 
the  cooked  prune. 

These  astonishing  results  represent  but  a  portion 
—  indeed  a  minor  portion  —  of  the  achievements  of 
one  man  during  a  few  years  of  work,  and  they  afford 
an  excellent  illustration  of  the  possibilities  of  plant- 
breeding.  The  method  by  which  they  have  been 
brought  about  is  simplicity  itself:  variation  and  selec- 
tion are  the  two  processes  which  produce  all  these 
results.    We  may  now  examine  them  more  in  detail. 

It  is  a  familiar  fact  that  every  plant  shows  some 
variation  (since  no  two  plants,  or  leaves  even,  are 
alike),  and  it  has  been  discovered  that  variation  obeys 
certain  laws.  It  not  only  confines  itself  within  certain 
limits,  but  there  is  a  certain  average  form  or  type 
around  which  the  variations  group  themselves.  This 
may  be  made  clear  by  means  of  a  diagram.  If  we 
count  the  number  of  rays^  in  a  large  quantity  of 
daisies  (the  Common  Ox-eye  Daisy),  we  may  find  that 
it  varies,  let  us  say,  from  five  to  thirty- seven.  If  we 
sort  them  into  piles,  putting  into  the  first  pile  all  those 
with  five  petals,  into  the  second  all  those  with  six, 
and  so  on,  we  shall  find  that  the  pile  containing 
those  with  twenty -one  petals  is  the  largest.  If,  now, 
we  string  the  daisies  in  each  pile  on  an  upright  wire, 
so  as  to  form  vertical  columns  of  them,  we  shall  get 

I  The  rays  are  the  white  outer  parts,  usually  called  "petals." 
AA 


418 


EXPERIMENTS    IV ITS  PLANTS 


the  series  represented  by  the  upright  lines  in  Fig.  237. 
The  highest  pile  is  the  one  containing  those  with 
twenty- one  rays,  and  the  size  of  the  piles  decreases 
in  both  directions  from  this:  those  which  contain 
daisies  with  five  and  thirty- seven  rays  are  the  smallest 
and  represent  the  two  extremes.  When  we  draw  a 
line  over  the   tops   of  the  piles,  we   get  a   curve   of 


Zl  U  it  2S  lb  27  26  i9  .10  0>   32.33  . 

237.    Curve  of  variation ;  the  result  of  sorting  daisies  into 
piles  according  to  the  number  of  rays  they  possess. 

very  characteristic  form.  It  has  been  found  that,  no 
matter  what  feature  of  an  organism  we  study  in  this 
way,  we  get  practically  the  same  sort  of  curve  (the 
only  apparent  exception  being  partial  curves  and 
double  curves).  This  curve,  therefore,  becomes  of 
great  interest,  especially  as  it  is  found  that  it  can 
be  expressed  by  a  mathematical  formula  and  that 
the  variation  obej^s  certain  mathematical  laws.  The 
mathematical,  or  statistical,  study  of  variation  has 
now  become  an  important  branch  of  biology. 


MAKING    NEW    KINDS   OF    PLANTS 


419 


It  may  be  remarked  that  a  curve  like  that  shown 
in  Fig.  238  would  indicate  that  the  species  was  evolving 


Z    17   18    19  »  ai    it  23  2t  25  2b  27  2a  29  JO  31  32  30  3«  35  3b  37  3839  40  -Jl  ^^43  ■♦435 


238.    Asymmetrical  curve  of  variation. 

in  the  direction  of  a  larger  number  of  rays,  since  it 
shows  more  individuals  above  than  below  the  type 
in  respect  to  the  number  of  rays.    A  curve  like  that  in 


5    fo    7    8    9   10  11  U    13  t*  15  Ife  ?7  18  )9  20  21    22  13Z1  25  ^li  27  28  29  3031  3^3J34J5 

239.    DoiTble  c^^rve  of  variation. 

Fig.  239  would  indicate  a  splitting  up  of  the  species  into 
a  form  with  thirteen  and  a  form  with  twenty- one  rays, 


420  EXPERIMENTS    WITE  PLANTS 

The  variations  just  discussed  are  the  ordinary 
kind  and  may  be  called  fluctuating  variations  (because 
they  fluctuate  around  a  mean,  or  average  type)  to 
distinguish  them  from  sudden  variations  or  sports 
(e.  g.,  reversions  and  monstrosities),  which  are  sudden 
and  apparently  lawless  deviations  from  the  type  and 
only  occur  occasionally;  fluctuating  variations,  on  the 
other  hand,  occur  everywhere  and  in  all  plants.  A 
Peach  tree  occasionally  produces  a  branch  which 
bears  only  nectarines;  this  is  called  a  sport.  If  the 
branch  be  cut  off  and  used  as  a  cutting  it  will  produce 
a  Nectarine  tree.  Occasionally  a  branch  of  this  may 
produce  peaches:  this  return  to  the  original  condition 
is  termed  atavism,  or  reversion,  and  is  also  apt  to  occur 
in  plants  which  are  not  known  to  have  originated 
as  sports.  When  a  sudden  variation  originates,  as 
in  this  instance,  from  a  single  bud  on  a  plant,  it  is 
called  a  "bud -variation."  The  various  Moss  Roses, 
many  kinds  of  Chrysanthemums,  many  variegated 
plants,  etc.,^  have  originated  in  this  way.  The  word 
sport  is  usually  applied  to  bud -variations,  but  is 
not  necessarily  limited  to  them.  It  may  be  used  for 
any  kind  of  sudden  variation.  The  term  monstrosity  is 
commonly  used  to  designate  a  sudden  variation  which 
has  the  appearance  of  an  abnormality  or  deformity; 
as,  for  example,  when  a  stem   becomes  flattened   and 

iSee  Bailey:  "Plant  Breeding,"  first  edition  (1895)  or  second  edition 
(1902),  Lecture  IV.  (This  lecture  does  not  appear  in  the  third  edition , 
1904.) 


MAKING    NEW    KINDS    OF     PLANTS  421 

fan -like  as  in  the  Cockscomb,  or  when  the  edges  of 
the  leaf  unite  and  cause  it  to  assume  the  form  of  a 
pitcher,  as  happens  not  infrequently  in  various  plants. 

Sadden  variations  may  or  may  not  come  true  to 
seed.  The  greatest  importance  is  attributed  to  them 
by  Professor  de  Yries,  as  will  be  seen  later. 

Whoever  wishes  to  improve  plants  must  be  on 
the  alert  to  seize  upon  variations,  whether  they  be 
of  the  ordinary  fluctuating  kind  or  sudden  variations. 
Ordinarily  only  favorable  ones  will  be  preserved,  but 
when  these  do  not  occur  the  plant- breeder  may  con- 
tinue to  propagate  the  most  variable  individuals, 
hoping  that  in  time  favorable  variations  will  occur. 

By  varying  the  conditions  of  culture^  and  climate 
(described  in  Chapter  VIII),  it  is  possible  for  the 
breeder  to  produce  variations  in  the  desired  direction, 
or,  as  he  says,  "break  the  type."  Some  plants  respond 
very  readily  to  that  treatment:  others  do  not.  In 
general,  however,  this  is  a  tedious  process  and  of 
very  small  value  as  compared  with  crossing. 

By  crossing,  the  breeder  can  create  almost  endless 
variations  and  at  the  same  time  direct  them  in  the 
desired  channels.  Crossing  means  the  fertilization  of 
a  plant  with  pollen  from  a  different  variety  or  species. 
The  result  of  the  cross  is  called  a  hybrid.- 

1  See  an  article  by  Webber  in  the  Year  -  Book  of  the  United  States 
Department   of   Agriculture    for   1896. 

2  See  Bailey:  "Plant  Breeding."  See  footnote  on  page  420.  Also  an  article 
by  Swingle  and  Webber  in  the  Year -Book  of  the  United  States  Department 
of  Agriculture  for  1897. 


422  tiXPEBIMENTS    WITH  PLANTS 

The  hybrid  may  resemble  both  parents  and  possess 
intermediate  characters.  This  is  the  more  usual  con- 
dition, and  may  show  itself  as  a  mixing  of  the 
characters,  as  when  a  red  flower  crossed  with  a 
yellow  one  gives  a  spotted  flower  with  red  and  yellow 
spots  standing  side  by  side;  or  it  may  result  in  a 
blending  of  characters,  giving  in  this  case  a  uniformly 
orange -colored  flower;  or,  finally,  we  may  have  the 
characters  both  mixed  and  blended,  giving  orange- 
colored  petals  with  red  and  yellow  spots. 

The  hybrid  frequently  resembles  one  parent  much 
more  than  the  other,  sometimes  showing  the  char- 
acters, of  one  parent  only. 

It  very  frequently  happens  that  the  hybrid  is  of 
greater  size  and  vigor  than  either  of  the  parents. 
A  good  illustration  of  this  is  seen  in  Fig.  231.  Another 
case  in  point  is  the  Shasta  Daisy  (Fig.  240),  which 
also  shows  how  the  qualities  of  diverse  parents  may 
be  skilfully  combined.  It  is  the  result  of  a  cross 
between  the  common  Field  Daisy  of  the  eastern  United 
States  ( chosen  for  its  free  -  flowering  habit ) ,  a 
European  Daisy  (chosen  for  its  vigor  and  size),  and 
a  Japanese  Daisy  (chosen  for  the  peculiar  dazzling 
white  luster  of  its  petals).  The  hybrid  proved  larger 
than  its  parents  and,  by  selection,  flowers  have  been 
obtained  which  under  good  cultivation  reach  a  diameter 
of  six  inches  (see  Fig.  240,  which  shows  the  Shasta 
and  the  American  parent;  the  English  and  Japanese 


240.    The  Shasta  Daisy  and  one  of  its  parents,  the  American  Field  Daisy. 
About  one-half  natural  size. 


341.    Shasta  Daisies,  showing  variatiou  due  to  crossing. 


MAKING    NEW    KINDS    OF    PLANTS 


425 


parents  are  about  the  size  of  the  American).  Not 
only  so,  but  the  good  qualities  of  the  parents  have 
all  been  retained  and  the  bad  ones  eliminated.  The 
hybrid  is  very  hardy,  blooms  abundantly  and  con- 
tinues to  blossom  throughout  the  season  (in  California 
nearly  all  the  year).  The  great  white  flowers  stand 
up,  each  on  a  separate  stalk,  two  to  three  feet  long, 
making  splendid  cut -flowers,  and  remain  fresh  for 
two  weeks  after  cutting.  The  petals  have  the  peculiar 
whiteness  and  luster  of  the  Japanese  parent.  More- 
over, the  plants  are  perennial  and  bear  more  and  more 
abundantly  each  season. 

Not  content  with  mere  increase  in  size  and  pro- 
ductiveness, the  originator,  Mr.  Burbank,  endeavored 
to  obtain  new  forms 
of  rays  (or  petals) . 
Among  the  hybrids 
which  appeared  were 
such  forms  as  are 
illustrated  in  Fig. 
241.  By  selection  of 
these  a  number  of 
different  kinds  of  ex- 
ceeding beauty  and 
interest     have    been 

secured,     comparable  --^2.    Double  Shasta  Daisy. 

to  the  forms  of  Chrysanthemums.  By  continued  selec- 
tion the  double  form  shown  in  Fig.  242  was  obtained. 


24J.     Variation  iu  leaves  of  hybrid  Blackberries,  all  from  the  seed  of  one  plant. 


MAKING    XEW    KINDS    OF     PLANTS 


427 


All  these  are  propagated  by  cuttings,  so  that  there  is 
no  trouble  over  iixation  (see  p.  433) .  Thus  in  the  short 
space  of  a  few  years  a  disagreeable  weed  has  been 
transformed  into  a  splendid  ornament  of  the  garden! 


Variation  in  stems  of  hybrid  Blackberries,  all  from  the  seed  of  one  plant. 


One  of  the  most  striking  traits  of  hybrids  is  their 
tendency  to  vary  widely.  Figures  243  and  244,  show- 
ing the  variation  in  leaves  and  stems  of  Blackberry 
hybrids  all  raised  from  the  seed  of  a  single  plant, 
will  repay  careful  study  (the  colors  of  the  stems  are 
as  variable  as  the  forms) ;  what  points  of  difference 
can  you  distinguish  in  these  specimens?  The  parent 
forms  are  not  shown  in  this  case,  but  in  Fig.  245, 
illustrating  the  leaves  of  hybrids  between  the  Oriental 


428  EXPERIMENTS    WITH   PLANTS 

and  the  Opium  Poppy  (the  two  common  garden  sorts), 
one  can  trace  clearly  the  influence  of  the  parents  and 
see  how  their  characters  combine  to  produce  a  great 
diversity  of  forms.  These  leaves  I  took  from  plants 
growing  together  in  the  same  bed  in  Mr.  Burbank's 
garden. 

Study  the  hybrids  which  are  to  be  found  in  our 
gardens,  especially  the  Pansies,  Cannas,  etc.,  and  see 
whether  they  are  variable.  These,  it  should  be  remem- 
bered, have  their  variability  reduced  as  much  as 
possible  by  "fixing"  before  they  are  put  on  the 
market. 

Mr.  Burbank's  experience  with  Beans  illustrates 
how  the  tendency  to  vary  causes  practical  difficulties. 
On  crossing  the  Cranberry  Bean  (which  has  red  pods 
and  white  beans)  with  the  Horticultural  Pole  Bean 
(which  has  red  pods  striped  with  white  and  red-and- 
white  beans),  a  single  seed  was  obtained:  this  was 
planted,  and  produced  a  plant  having  pods  of  mixed 
character  but  with  all  the  beans  black.  When  these 
were  planted,  an  astonishing  variety  of  plants  appeared: 
some  were  Pole  Beans  running  up  twenty  feet,  others 
were  Bush  Beans;  some  spread  out  on  the  ground 
but  a  few  inches  in  height;  these  latter  in  some 
cases  produced  pods  taller  than  themselves.  The 
variety  of  pods  was  bewildering,  while  the  beans 
themselves  represented  in  size,  shape,  color  and  mark- 
ings   almost    every    known    sort.     Professor    Bailey 


MAKING    NEW   KINDS    OF    PLANTS 


429 


records  a  similar  experience  with  Squashes  ^  in  which 
the  seeds  of  one  plant  gave  one  hundred  and  ten 
kinds  distinct  enough  to  be  named  and  recognized. 
Such  hybrids  represent  extremely  variable  types  in 
which  it  is  practically  impossible  to  fix  anything. 


245.    Hybrid  Poppy  leaves.    At  the  left,  a  leaf  of  the  Oriental  Poppy;    at  the  right, 
a  leaf  of  the  Opium  Poppy;    in  the  center  a  group  of  leaves  of  the  hybrids. 

To  successfully  combine  the  qualities  of  different 
plants  by  crossing  requires  a  rare  degree  of  skill 
and  judgment.  It  might  seem,  perhaps,  as  though 
it  would  be  a  comparatively  simple  matter  to  make 
all  possible  Plum  crosses,  for  example,  and  select  the 
best.    But  in  practice  it  is  found  that  the  number  of 

1  Bailey:  "Plant  Breeding,"  third  edition,  1904,  p.  78. 


430  EXPERIMENTS    WITH  PLANTS 

possible  combinations  is  so  great,  and  the  results  so 
bewilderingly  varied,  that  short-cut  methods  must  be 
used.  In  other  words,  the  plant- breeder  must  be  able 
to  iadge  beforehand  what  the  result  of  crossing  certain 
plants  will  be,  in  order  not  to  waste  time  on  profitless 
experiments.  It  is  just  here  that  the  opportunity 
comes  for  the  highest  skill,  based  not  only  on 
empirical  knowledge  but  on  a  profound  insight  into 
the  laws  of  heredity  and  variation  and  a  sound 
philosophy  of  nature.  Moreover,  there  must  be  a 
clear-cut  ideal  present  in  the  mind  of  the  worker, 
toward  which  he  persistently  strives  and  from  which 
he  refuses  to  diverge  even  for  the  most  promising 
side  issues.  He  wields  forces  which  at  best  are  but 
partly  understood;  they  manifest  themselves  in  be- 
wildering variety:  to  hold  persistently  to  a  definite 
ideal  is  the  surest  path  to  success. 

There  is  no  mystery  in  the  method  by  which  these 
crosses  are  made.  Mr.  Burbank's  methods  of  pollina- 
ting Plums  will  serve  to  illustrate  the  matter.  The 
flowers  which  are  to  furnish  the  pollen  are  carefully 
gathered  a  daj^  or  so  beforehand,  -the  pollen  sifted 
out  and  kept  in  a  cool  place.  The  tree  to  which  the 
pollen  is  to  be  applied  is  deprived  of  most  of  its 
blossoms,  in  order  that  the  remainder  may  be  sure 
to  develop  and  that  there  may  not  be  too  many  to 
look  after  properly.  The  blossoms  which  remain  on 
the   tree   are    prepared    by   cutting    away   the   petals 


MAKING    NEW   KINDS    OF    PLANTS  431 

with  the  attached  anthers,  as  shown  in  Fig.  246.    By 

comparing  with  Fig.  161,  one  can  see  just  what  part 

of  the  flower  is  removed.     The  pistils  and 

stigmas    are    left   exposed    and    uninjured. 

This  is  done  before  the  buds  are  open.    Mr. 

Burbank  finds  that  the  time  when  the  hum 

of  the  bees  is  first  heard  in  the  trees  is  the 

best   for    pollination,    as    the    stigma    then 

seems  to  be  in  a  receptive   condition.    The 

pollen    is    apjjlied    by    simply    dipping   the 

finger  into  it  and  touching  it  to  the  stigmas. 

The  tree  is  then  left  to  itself:   the  bees  do 

not   visit    the    flowers:    the   petals    are  not 

present   to    attract  them,    and    there    is    no 

foothold   for   them    should   they  come.     So     soms showing 

.  the  manner  in 

there  is  little  danger  that  any  other  pollen     ^/g^'^t^V'Xe; 
will  be  brought.    (Where  it  is  important  to     ric\ed^sta- 

1,1  .  1.  l.^  n  mens,  are  cut 

know  the  exact  parentage,  the  flowers  may     away  prepar- 
be  covered  with  bags,  as  described  on  page     nation. 
289:    for  practical   purposes  this   seems   to    be,  as    a 
rule,  unnecessary.) 

The  application  of  pollen  may  or  may  not  result 
in  the  setting  of  fruit.  If  the  parents  are  of  very 
dissimilar  species,  fruit  will  not  set  at  all:  or  it  may 
do  so  occasionally,  say  once  in  a  thousand  times. 
Sometimes  fruit  appears  to  set,  but  on  ripening  it 
is  found  to  contain  no  seeds:  again,  seeds  are  pro- 
duced which  look  well  but  are  incapable  of  germina- 


432  EXPEBIMENTS    WITH  PLANTS 

tion.  Or  the  seeds  may  germinate,  but  the  young 
plants  prove  so  weak  that  they  cannot  be  raised. 
Even  in  favorable  cases  not  all  the  flowers  yield  seed, 
but  if  only  a  few  good  seeds  are  obtained  it  is 
sufficient  for  a  start. ^ 

All  the  seeds  from  the  tree  are  carefully  saved 
and  sown:  as  soon  as  they  come  up,  the  judgment 
of  the  breeder  comes  into  play.  From  the  foliage  he 
is  able  to  judge  beforehand  what  the  fruit  will  be, 
and  so  save  needless  time  and  trouble  by  preserving 
only  the  most  promising.  In  order  to  make  these 
fruit  quickly,  they  are  cut  off  near  the  ground  when 
only  a  few  inches  high  and  grafted  upon  other  trees, 
where  they  often  proceed  to  flower  the  third  year 
from  the  seed.  When  the  blossoms  appear,  another 
important  question  must  be  decided.  Shall  they  be 
pollinated  with  the  pollen  of  a  sister  hybrid,  or  of 
one  of  the  two  parents,  or  of  another  variety?  Here, 
again,  comes  the  opportunity  for  the  greatest  skill 
and  judgment,  amounting  in  its  highest  manifestations 
to  positive  genius,  and  yielding  in  the  brief  space  of 
a  few  years  results  which  a  lesser  skill  could  not 
compass  in  a  lifetime.  A  successful  plant- breeder 
judges  plant  character  as  a  great  organizer  judges 
human  character,  partly  by  evident  signs,  partly  by 
an  intuitive    feeling   for  the  more    subtle    differences 

iThe  more  difficult  the  cross  the  greater  should  be  the  number  of 
plants  used.  Thus,  Mr.  Burbank  has  succeeded  by  using  large  numbers  in 
crossing  the  Tobacco  and  the  Petunia,  a  very  difficult  cross  indeed. 


MAKING    NEW    KINDS    OF    PLANTS  433 

which  can  hardly  be  defined  in  words  and  which  may 
be  completely  hidden  from  the  ordinary  observer. 

When  the  fruit  appears  it  is  carefully  examined, 
compared  and  tested :  the  seeds  of  the  best  are  pre- 
served and  the  rest  are  destroyed :  out  of  a  thousand  or 
more,  only  one  or  two  may  survive  the  rigid  tests 
which  are  applied.  The  seeds  of  these  are  sown  and 
the  best  again  selected.  This  is  continued  indefinitely 
until  a  desirable  variety  is  secured,  or  until  it  be- 
comes evident  that  no  good  results  are  to  be  expected: 
in  that  case  the  plants  are  all  destroyed,  and  the 
work  of  years  ends  in  nothing. 

It  is  very  evident,  therefore,  that  hybridization, 
with  all  its  marvelous  results,  is  but  the  beginning 
of  plant- breeding.  All  that  it  does  is  to  furnish 
variations.  To  seize  upon  these,  even  though  they 
be  slight,  and  divert  them  into  the  proper  channels, 
to  intensify  the  good  and  suppress  the  undesirable 
qualities,  until  the  ideal  is  reached,  is  the  task  of 
selection.  ^ 

When  plants  can  be  propagated  by  cuttings,  grafts, 
bulbs  or  other  vegetative  parts  ^  the  ideal  once  achieved 
is  easily  maintained,  for  plants  so  propagated  "come 
true,"  or,  in  other  words,  maintain  the  characters 
of  the  parent  plant,  with  little  variation.  Far  other- 
wise, however,  with  plants  which  are  propagated  by 

1  See  articles  in  the  Year -Book  of  the  United  States  Department  or 
Agriculture  for  1898,  by  Webber;  for  1901,  by  Hays;   for  1902,  by  Webber. 

2  1.  e.,  leaves,  corras,  rootstocks,  roots,  tubers,  etc. 

BB 


434  £XPEBI3fENTS    WITH  PLANTS 

seed;  for,  after  selection  has  achieved  the  ideal,  it 
has  still  the  task  of  "fixing"  it  so  that  it  will  come 
true  to  seed. 

In  order  to.  achieve  our  ideal,  we  have  had  to  set 
in  motion  the  tendency  to  variation,  or,  as  we  say,  we 
have  "broken  the  type."  When  the  ideal  is  achieved, 
this  same  tendency  which  we  have  set  in  motion  will 
destroy  our  ideal  unless  selection  is  able  to  suppress 
the  tendency  and  so  "fix  the  type,"  or,  in  other 
words,  bring  the  plant  again  to  a  state  of  equilibrium. 
This  we  can  do  to  a  great  extent,  but  not  so  fully 
that  continued  selection  is  unnecessary.  And  it  often 
happens  that,  after  an  ideal  is  achieved,  years  elapse 
before  it  is  sufficiently  fixed  to  put  it  on  the  market. 

The  great  possibilities  of  selection  are  well  illus- 
trated in  the  case  of  corn -breeding  as  carried  on 
by  Professors  Hopkins  and  Shamel  at  the  Illinois 
Experiment  Station.^  At  the  same  time,  these  ex- 
periments illustrate  the  great  value  of  a  thorough 
acquaintance  with  the  plant  and  its  possibilities,  com- 
bined with  a  knowledge  of  the  desirability  of  the 
various  possible  lines  of  improvement  as  shown  by 
the  demands  of  the  market.  Suppose  you  were  to 
undertake  the  production   of  an  improved  variety  of 

1  See  "Com  Culture  and  Breeding,"  Thirteenth  Report  Kansas  Board  of 
Agriculture,  XVHI,  785-817.  Also  Bulletin  No.  82,  Illinois  Agricultural 
Experiment  Station,  525-539.  Also  articles  by  Professor  Shamel  in  the 
Cosmopolitan  for  May,  1903;  by  W.  S.  Harwocd  in  WorkVs  Work 
for  September,  1902,  and  by  C.  P.  Hartley  in  Year  -  Book  of  the  United  States 
Department   of   Agriculture   for    1902. 


MAKING    NEW   KINDS    OF    PLANTS  435 

Corn.  You  would  have  before  you  the  possibility 
of  improving  along  any  one  of  the  following  lines: 

1.  Increased  yield. — In  the  ordinary  corn-field  one 
well -developed  ear  to  a  hill  means  a  yield  of  about 
fifty-five  bushels  to  the  acre;  two  ears  means  over 
one  hundred  bushels,  three  ears  over  one  hundred 
and  fifty  bushels.  Now  in  Illinois,  where  a  great 
corn- breeding  movement  is  in  progress,  it  was  found 
that  there  are,  on  the  average,  more  than  two  stalks 
to  the  hill,  each  capable  of  bearing  a  well -developed 
ear;  yet  the  average  yield  is  less  than  thirty  bushels 
to  the  acre.  The  trouble  is  partly  due  to  barren  stalks, 
partly  to  poorly  developed  ears.  Consequently  an 
effort  was  made  to  improve  the  Corn  in  these  respects. 
Now,  it  was  found  that  a  barren  stalk  produces  more 
pollen  than  a  productive  one,  since  none  of  its 
strength  goes  to  producing  an  ear:  consequently  it 
fertilizes  a  larger  number  of  plants  than  the  pollen 
from  a  productive  stalk:  the  result  is  that  the  tendency 
to  barrenness  is  consequently  on  the  increase.  Obvi- 
ously one  thing  to  do  was  to  go  through  the  fields 
looking  for  barren  stalks,  and  cutting  off  their  tassels 
before  the  pollen  was  shed.  In  this  way  the  per- 
centage of  barren  stalks  was  noticeably  decreased. 

Another  thing  to  be  done  was  to  select  seed  from 
the  best  ears.  To  do  this  properly  requires  skill  and 
experience.  Not  only  the  size  and  shape  of  the  ear 
but  the  manner  in  which  it  is  filled  out,  especially  at 


436  EXPERIMENTS    WITS  PLANTS 

the  end;  the  weight  and  color  of  the  grain  and  of 
the  cob;  the  number,  size  and  shape  of  the  kernels, 
and  many  other  points  must  be  considered. 

It  is  not  sufficient  to  select  the  best  ears:  we 
must  know  which  of  the  selected  ears  can  transmit 
its  good  qualities  in  the  highest  degree;  in  other 
words,  we  must  determine  what  is  known  as  the 
hereditary  percentage^  (i.  e.,  the  percentage  of  off- 
spring which  inherit  the  desirable  characters).  For 
this  purpose  the  kernels  from  each  ear  are  sown  by 
themselves  in  a  separate  row,  so  that  the  offspring 
of  the  different  ears  can  be  readily  compared. 

The  poor,  or  barren  stalks,  and  the  suckers  are 
removed  before  the  tassel  appears.  Since  the  pollen 
is  carried  by  the  wind  for  about  a  mile,  it  is  an 
obvious  advantage  to  have  the  field  well  separated 
from  other  fields  likely  to  contaminate  it.  In  the 
fall  the  seed  for  next  year's  crop  is  selected  from 
the  rows  which,  all  things  considered,  give  the  best 
results. 

The  results  of  this  work  may  be  illustrated  by  the 
experience  of  a  farmer  in  southern  Illinois  who  was 
induced  to  plant  three  hundred  acres  with  improved 
Corn  seed.  These  three  hundred  acres  yielded  thirty 
bushels  per  acre  more  than  the  fields  planted  with 
unimproved    seed,    or,    in    other   words,    gave    about 

1  The  hereditary  percentage  is  one  of  the  most  important  matters  in 
selection   and   is  only  too   commonly   lost   sight   of  by   breeders. 


MAKING    NEW    KINDS    OF    PLANTS  437 

double  crops.  Now,  as  the  cost  of  labor,  etc.,  remains 
the  same,  whether  improved  or  unimproved  seed  is 
planted,  the  gain  is  all  clear  profit.  An  increase  of 
only  ten  bushels  per  acre  in  the  yield  of  corn  would 
mean  an  increase  in  our  national  wealth  of  over  four 
hundred  and  eighty  million  dollars  a  year. 

2.  Quality. — A  bushel  of  corn,  weighing  fifty-six 
pounds,  contains  approximately: 

36  pounds  dry  starch,  worth  \%  cents  per  pound. 

7  pounds  gluten,  worth  1  cent  per  pound. 

5  pounds  bran  or  hull,  worth  %  cent  per  pound. 
4%"  pounds  germ,  40  per  cent  of  which  is  oil,  worth  5  cents  per  pound. 
3X  pounds  water  and  soluble  matter,  worth  0  cents  per  pound. 

Which  one  of  these  constituents  shall  we  increase 
to  improve  the  quality  of  the  corn?  We  might  en- 
deavor to  increase  the  percentage  of  oil,'  since  this 
is  the  most  valuable  component.  We  must,  however, 
first  consider  whether  any  one  will  pay  a  correspond- 
ingly higher  price  for  corn  containing  more  oil.  As 
a  matter  of  fact,  a  company  which  buys  about  fifty 
million  bushels  of  corn  per  year  offered  to  pay  a 
higher  price  for  corn  containing  a  higher  percentage 
of  oil:  an  increase  in  oil  of  one  pound  per  bushel 
would  increase  the  price  of  corn  five  cents  per 
bushel.  The  Illinois  Experiment  Station  succeeded  in 
increasing   the    amount   of   oil    from  4.7  per  cent  to 

1  The  oil  is  valuable  as  a  component  of  "artificial  rubber"  used  for 
electrical  purposes,  and  is  of  especial  importance  in  view  of  the  decrease  of 
the  world's  supply  of  rubber.  The  oil  is  also  used  for  lubricating:  purposes, 
for  adulterating  olive-oil,  as  well  as  in  the  manufacture  of  soaps,  paints,  etc. 


438  EXPERIMENTS    WITH   PLANTS 

nearly  7  per  cent  in  six  years.  The  method  at  first 
involved  a  rigid  chemical  analysis  of  the  ears  and 
selection  of  the  best.  Afterward  it  was  found  that 
for  practical  purposes  the  chemical  analysis  could  be 
dispensed  with:  since  the  germ  contains  most  of  the 
oil,  it  is  only  necessary  to  select  the  kernels  with 
the  largest  germs.  On  the  other  hand,  Corn  with 
a  lower  oil -content  is  wanted  as  a  feed  for  hogs,  since 
it  produces  harder,  firmer  bacon.  So  the  Station  pro- 
ceeded by  selection  to  decrease  the  amount  of  oil 
to  less  than  2  per  cent.  It  would,  therefore,  depend 
on  market  conditions  whether  w^e  should  try  to  increase 
or  decrease  the  amount  of  oil  in  the  corn. 

In  the  same  way  we  should  breed  to  increase  the 
amount  of  protein  if  the  corn  is  to  be  used  for  food, 
but  to  decrease  it  if  the  corn  is  to  be  used  for  starch. 
The  Station  workers  were  able  to  increase  the  pro- 
tein from  10.92  per  cent  to  16  per  cent  in  about  six 
years,  and  to  decrease  it  to  Q,QQ  per  cent  in  the  same 
length  of  time.  Here,  again,  it  is  found  practicable 
for  ordinary  purposes  to  dispense  wdth  chemical 
analysis  and  select  those  kernels  w^hich  have  the  white, 
starchy  part  around  the  germ  best  or  least  developed, 
according  to  which  is  desired:  this  is  possible  be- 
cause the  protein  is  almost  all  contained  in  the  germ 
and  in  the  horny  outer  part  of  the  kernel,  w^hile 
the  starch  is  practically  all  in  the  white  portion  which 
lies  between  them. 


MAKING    NEW   KINDS    OF    PLANTS  439 

3.  Size,  shape,  color,  etc. — Some  of  the  points 
already  mentioned  might  appropriately  come  under 
this  head  also:  in  addition,  we  may  mention  that  the 
Station  has  increased  the  length  of  shank  nearly  two 
feet  in  five  years'  selection,  and  has  been  able  to 
shorten  or  lengthen  the  ear,  to  increase  or  decrease 
the  width  of  the  ear  and  to  raise  or  lower  the  position 
of  the  ears  on  the  stalks.  Further  changes  in  the 
appearance  of  the  Corn  plant  could  be  made  almost 
indefinitely  if  they  seemed  desirable. 

The  color  of  the  kernel  is  of  some  importance; 
some  markets  demand  golden  yellow  meal  and  others 
white:  furthermore,  manufacturers  of  white  meal  pre- 
fer white  to  red  cobs,  since  debris  from  the  latter  is 
apt  to  color  the  meal.  Hard  kernels  from  which  the 
germ  readily  separates  are  desired  by  hominy- makers. 

Large  ears  (one  to  a  plant)  are  desirable  when  the 
corn  is  to  be  shucked  by  hand  and  shelled  or  sold 
for  milling.  Smaller  ears  (two  or  more  to  a  stalk) 
are  desirable  where  machinery  is  to  be  used  and  the 
ears  fed  to  cattle. 

4.  Earliness,  etc. — To  obtain  early  varieties  is,  in 
general,  a  very  difficult  matter.  Two  things  must  be 
secured;  first,  hardiness,  i.  e.,  resistance  to  frost, 
sudden  changes,  etc.;  second,  the  ability  to  ripen 
fruit  in  a  shorter  season.  This  is  a  difficult  com- 
bination to  obtain:  nevertheless,  the  Corn -belt  has 
moved  rapidly  northward   in   the   last   fifteen   years. 


440  EXPERIMENTS    WITH  PLANTS 

The  original  home  of  the  Corn  was  in  Central  America, 
and  it  has  moved  all  the  way  to  Lake  Superior,  with 
the  consequent  gain  in  hardiness  and  ability  to  ripen 
quickly,  as  the  result  of  selection  by  man. 

5.  Adaptation  to  peculiar  regions  or  conditions. — 
There  are  thousands  on  thousands  of  acres  of  land 
where  Corn  cannot  now  be  grown,  simply  because  the 
soil  contains  too  much  alkali.  Yet  the  same  soil  will 
grow  Sugar  Beets  excellently.  Why  should  it  not 
be  possible  to  breed  a  race  of  Corn  tolerant  of  alkali? 
A  race  of  Corn  resistant  to  drought  would  also  prove 
of  great  value. 

6.  Resistance  to  disease,  etc. — An  immense  amount 
of  damage  is  annually  done  by  Corn  -  smut  (see 
page  400) .  Yet  in  the  most  badly  infested  fields  some 
sound  ears  will  be  found.  By  careful  selection  of 
these  a  resistant  variety  might  be  obtained. 

Any  one  who  should  attempt  the  improvement  of 
Corn  on  the  old  hit-and-miss  principle  might  possibly 
stumble  on  good  results,  but  the  chances  would  be 
largely  against  him.  To  be  sure  of  success,  he  must, 
after  taking  into  account  such  considerations  as  those 
mentioned  above,  decide  which  particular  line  of  im- 
provement is  most  feasible  and  most  profitable,  and, 
after  formulating  a  definite  ideal,  work  persistently 
toward  it.  The  greater  his  skill  and  the  more  accurate 
his  judgment  the  sooner  will  he  accomplish  his 
aim;  in  this  work  it  is  impossible  to  set  any  limits 


MAKING    KUW    KINDS    OF    PLANTS  441 

to  the  results  which  are  obtainable  in  the  hands  of  a 
master.  ^ 

From  the  standpoint  of  economics,  plant-  and 
animal -breeding  is  of  the  highest  importance,  since 
it  adds,  in  a  superlative  degree,  to  the  permanent 
wealth  and  increased  material  happiness  of  a  nation. 
The  work  of  our  successful  plant-  and  animal -breeders 
cannot  be  too  highly  estimated,  and  it  is  a  pity  that 
it  so  seldom  results  in  much  pecuniary  gain  to  them- 
selves. Government  work  in  this  line  has  been  totally 
incommensurate  with  the  importance  of  the  subject. 
The  United  States  Government,  however,  has  made  a 
beginning  by  establishing  a  laboratory  for  plant - 
breeding. 2 

The  whole  doctrine  of  plant- breeding  is  intimately 
connected  with  the  question  of  the  origin  of  species. 
Darwin,  seeking  an  explanation  of  this  question,  took 
his  cue  from  the  experience  of  plant-  and  animal- 
breeders,    and    conceived  that    species    may  originate 

lEven  in  unskilled  hands  good  results  may  often  be  obtained.  For  the 
remarkable  achievements  of  Canadian  school  -  children,  see  an  article  by 
George  lies,  "Teaching  Farmers'  Children  on  the  Ground,"  in  the  Wo7'ld^s 
Work  for  May,  1903. 

2  On  the  general  subject  of  plant -breeding,  see  articles  in  the  Year  -  Book 
of  the  United  States  Department  of  Agriculture  for  1899,  by  Webber  and 
Bessey;  for  1901,  by  Hays  (also  those  already  referred  to).  Also  the 
bibliography  in  Bailey's  "Plant  Breeding,"  also  articles  in  Country  Life  in 
America  for  July,  1903,  by  Bailey;  in  The  WorhVs  Work  for  1902  (Vol.  II, 
p.  1209),  by  Bailey,  and  in  the  Sunset  Magazine  for  December,  1901,  February 
and  April,  1902,  by  Wickson,  and  in  the  Century  for  March,  1907,  by  de  Vries, 
See  also  de  Vries:  "  Plant  Breeding." 


442  EXPERIMENTS    WITH  PLANTS 

in  nature,  just  as  forms  originate  in  the  garden,  by 
the   selection   of  ordinary  fluctuating  variation   alone. 

In  other  words,  an  ordinary  fluctuating  variation 
may  be  so  intensified  by  selection  as  to  form  a  distinct 
mark  of  difference  between  the  improved  and  the 
original  form:  when  all  the  intermediate  forms  have 
perished,  we  have  two  species  instead  of  one.  Darwin^ 
believed  that  species  originated  in  this  way  both  in 
the  garden  and  in  nature  (where  the  struggle  for 
existence  selects  the  fittest  and  destroys  the  rest), 
and  that  the  species  so  formed  remain  distinct. 
Professor  de  Vries  has  recently  called  this  view  in 
question  on  the  basis  of  some  very  remarkable  experi- 
ments.^ 

Selection  cannot  make   new  species,   he  declares, 

1  Darwin  likewise  believed  that  species  could  originate  by  sudden  varia- 
tion, but  was  inclined  to  lay  less  emphasis  on  this  mode  of  origin. 

2  In  these  experiments  (  which  have  lasted  over  twenty  years ) 
Professor  de  Vries  has  combined  in  brilliant  fashion  the  special  points  of 
superiority  of  various  methods.  The  plant  -  breeder  has  the  advantage 
of  being  able  to  grow  and  judge  large  numbers  of  individuals  in  a  limited 
space:  of  this  he  has  made  use.  The  animal  -  breeder  in  the  most  important 
cases  keeps  in  a  book  a  pedigree -record  of  each  individual  animal,  its 
characters  and  those  of  its  offspring.  Professor  de  Vries  has  also  done 
this  in  all  the  most  important  cases,  giving  a  number  to  each  bed,  other 
numbers  to  each  row  in  the  bed,  and  also  to  each  plant  in  every  row. 
Thus,  each  plant  receives  a  number,  and  a  record  is  kept  both  of  it  and 
its  offspring.  In  many  cases  the  seeds  of  each  separate  plant  were  sown 
in  separate  beds,  in  order  that  the  hereditary  percentage  might  be  clearly 
determined.  Most  careful  precautions  have  been  taken  to  prevent  crossing,  by 
enclosing  the  flowers  in  parchment  paper  bags.  Finally,  he  has  made 
extensive  use  of  the  statistical  methods  described  above  (p.  417)  and  thus 
discovered  many  important  principles  which  would  not  otherwise  have 
come    to    light. 


MAKING    N-EW   KINDS    OF    PLANTS  443 

either  in  the  garden  or  in  nature;  all  selection  can 
do  is  to  temporarily  intensify  the  selected  character 
and  increase  the  frequency  of  its  occurrence:  when 
selection  ceases  the  percentage  of  frequency  soon  falls 
to  the  original  figure  and  all  becomes  as  it  was 
before.  Moreover,  new  species  are  not  formed  gradu- 
ally, as  the  selection  theory  demands,  but  they  originate 
suddenly,  fully  formed  and  constant  from  the  start, 
without  any  intermediates  between  them  and  their 
parent- species.  As  there  are  no  intermediate  forms, 
it  is  useless  to  search  for  such  "missing  links,"  for 
they  never  existed.  This  mode  of  origin  of  species, 
which  he  calls  mutation^  he  has  observed  year  after 
year  in  his  garden  at  the  University  of  Amsterdam. 
It  occurs  in  one  of  the  Evening  Primroses  {G'Jnothera 
Lamarckiana,  or  Lamarck's  Evening  Primrose,  Figs. 
247  to  250),  which  each  year  produces  several  new 
species.  These  remain  constant  and  perfectly  distinct, 
and  never  produce  intermediates  between  themselves 
and  their  parent- species.  They  originate  without  any 
of  the  means  ordinarily  considered  necessary:  no  ex- 
tended lapse  of  time  is  demanded;  no  fluctuating 
variation,  crossing  or  struggle  for  existence  appear  to 
enter  directly  into  the  matter. 

It  is  not  to  be  supposed  that  this  process  can  be 
observed  in  the  majority  of  plants.  The  opponents  of 
Darwin  have  already  contended,  on  the  ground  of  care- 
ful  experimental    evidence,    that   species,    instead    of 


MAKING    NJUW   KINDS    OF    PLANTS 


445 


being  in  a  state  of  continual  slow  change,  are  con- 
stant. Professor  de  Vries,  as  the  result  of  his  own 
experiments,  believes  that  species  are  constant  except 
at  certain  mutation  periods  which  may  occur  only 
at  long  intervals,  perhaps  of  some  hundreds  of  years. 


^1 

wSIk^^ 

IH^^^n 

■  ■  -t 

l*^^ 

5^J£« 

f 

248.  Lamarck's  Evening  Primrose  at  the  riglit,  and  one  of  the  new  species  wliich  has 
arisen  from  it  (Dwarf  Evening  Primrose)  at  the  left.  The  bags  are  for  the  pur- 
pose of  excluding  insects  from  the  flowers  which  are  being  artificially  pollinated. 
Botanic  Garden  of  the  University  of  California. 

The  differences  between  the  new  species  and  the 
parent  form  may  be  great  or  small:  it  does  not 
matter  which  they  are,  if  only  they  are  fixed  and 
constant.  Fig.  248  shows  a  striking  difference  in 
appearance  between  the  parent- species  and  one  of 
the  new  ones.  This  difference  cannot  be  overcome 
by  culture;  the  tallest  Dwarf  Evening  Primrose  is 
always  much  smaller  than  the  shortest  Lamarck's 
Evening  Primrose. 


446 


EXPERIMENTS    WITH  PLANTS 


In  Fig.  249  is  shown  a  leaf  of  Lamarck's  Evening 
Primrose  and  also  one  of  a  new  species  which  sprang 
from  it,  namely,  the  Broad  Evening  Piimrose  {(Eno- 

thera  lata).  The  latter  leaf 
is  not  only  somewhat  shorter 
and  broader,  but  is  blunt  in- 
stead of  pointed  at  the  tip. 
This  was  the  first  species  to 
originate  in  Professor  deVries' 
cultures.  The  seed  of  the 
Lamarck's  Evening  Primrose 
which  he  had  gathered  in  an 
abandoned  field  and  sown  in 
his  garden  produced,  the  first 
season,  among  a  large  num- 
ber of  ordinary  plants,  three 
which  were  distinctly  differ- 
ent from  the  rest  though 
closely  similar  to  each  other. 
They  had  broader,  less  pointed  leaves,  swollen  buds 
and  small  fruits:  the  stems  were  noticeably  small, 
weak  and  brittle:  at  the  tips  of  the  branches  the 
young  leaves  and  buds  were  collected  in  crowded 
rosettes  so  that  the  plants  were  at  first  called  "round- 
heads." Most  curious  of  all,  these  plants  were  entirely 
unable  to  produce  good  pollen.  Such  was  the  origin 
of  the  Broad  Evening  Primrose;  and  each  subsequent 
year,  as  the  seed  of  the  Lamarck's  Evening  Piimrose 


Leaf  of  Lamarck's  Evening 
Primrose  on  the  right,  and  of 
Broad  Evening  Primrose  on  the 
left. 


MAKING    NEW    KINDS    OF     PLANTS 


U7 


has  been  sown,  the  origm  of  the  Broad  Ev^ening 
Primrose  from  it  has  been  observed.  It  is  possible 
to  identify  this  and  other  new  species  in  the  seedling 
stage.  Fig.  250  shows  the  difference  in  the  appear- 
ance of  the  seedlings  of  (Enothera  Lamarckiana  and 
Oenothera    lata-,   while  the   strikingly  small   and  pale 


250.  Mutations  obtained  by  sowing  seed  of  Lamarck's  Evening 
Primrose.  TjT)ieal  Lamarck's  Evening  Primrose  on  the 
left,  Pale  Evening  Primrose  in  the  middle,  and  Broad 
Evening  Primrose  on  the  right. 

leaves  of  (Enothera  albida,  another  of  the  new  species, 
contrasts  with  both  the  other  two  species.  Most  of 
the  other  new  species  (of  which  there  are  several) 
can  be  identified  in  the  seedling  stage;  so  that  they 
can  be  early  transplanted  and  isolated  from  each 
other.  This  greatly  facilitates  the  handling  of  the 
specimens,  and  makes  it  possible  to  deal  wath  much 
larger  numbers  than  would  otherwise  be  the  case. 

Professor  de  Yries'  ideas  may  be  well  illustrated 
by  means  of  his  experiments  on  the  Bed  Clover. 
Every  one  knows  that  four-  and  five -leaved  Clovers  are 
found    occasionally.     Beginning  with    a    plant   which 


448  EXPEBIMENTtS    WITH   PLANTS 

bore  (in  addition  to  tiie  normal  leaves)  one  four- leaf 
and   one  five -leaf,  he  sowed   its   seed  and  found  that 
about  half  the  resulting  plants  bore 
(in  addition  to  normal  leaves)  four- 
and  five-leaves.  The  best  four  plants 
were   saved   and   their   seed   sown: 
this  time  80  per  cent  of  the  offspring 
had  the  four-  and  five-leaves 
and   a  few  six-  and  seven - 
leaves   made    their    appear- 
ance.   This  process  of  selec- 
tion    was     continued    until 

2")!.  Four-,  five- and  seven-  .        n  n      ii  nc 

leaved  Clover.  practically  all  the  onsprmg 
were  of  the  new  type  (i.  e.,  three-  to  seven- 
leaved,  Fig.  251),  or,  in  other  words,  the  seed 
came  true.  One  might  suppose  that  it  would 
now  be  possible  to  go  on  and  make  plants 
with  eight-and  nine-leaves.  The  attempt, 
however,  proved  fruitless.  The  limit  of  selec- 
tion was  reached  with  seven,  and  it  was  im- 
possible to  go  beyond  it.  On  the  ground  of 
many  similar  experiences,  he  comes  to  the 
conclusion  that  all  plants  have  a  limit  which 
is  quickly  reached  by  selection,  and  here  its 
power  ends.^  The  improved  race  is  not  a  species: 
it  has  no  constancy,  and  when  left  to  itself  quickly 
returns  to  the  original  type. 

1  He   believes   that   it   is   even   possible   to   tell   beforehand  how  much  a 
plant   can   be   improved  by   selection   and   where   the   limit   will   be 


MAKING    NEW    KINDS    OF    PLANTS 


449 


252.    Ten-leaved  Clover. 


There  is  a  well-known  freak  or  monstrosity  occur- 
ring in  many  species  of  plants  in  which  the  leaf 
splits  lengthwise  more  or  less  completely.  This  occm-s 
occasionally  among  the  Eed  Clover 
plants  just  described,  and  gives  rise 
to  leaves  with  higher  numbers  (four 
to  fourteen).  For  example,  a  five- 
leaf  may,  by  splitting,  become  a 
ten-leaf,  such  as  is  shown  in  Fig. 
252.  Professor  de  Vries  believes 
that  this  is  to  be  classed  as  a  mon- 
strosity and  is  quite  different  from  the  four-,  five-, 
six-,  and  seven-leaves  just  described,  which  are  due 
to  fluctuating  variation  and  obey  mathematical  laws. 
It  occurs  rarely,  appears  and  disappears  suddenly, 
bears  no  constant  relation  to  the  whole  number  of 
leaves,  and  is  to  be  classed  as  a  sudden  variation. 

Occasionally  a  Clover  leaf  is  met 
with  of  the  form  shown  in  Fig.  253. 
It  might  at  first  sight  be  classified 
as  one  of  the  abnormalities  just 
described.  When  we  consider,  how- 
ever, that  the  arrangement  of  the 
leaflet  in  two  rows,  one  each  side 
of  the  stalk,  is  the  same  as  that 
possessed  by  the  allies  of  the  Clover 
and  the  arrangement  which  the  ancestors  of  Clover 
itself  probably  had  a  long  time  ago,  it  seems  prob- 


253.    Atavistic  Clover 
leaf. 


cc 


450  JEXPEBIMENTS    WITH    PLANTS 

able  that  it  is  a  latent  character,  which  has  long  lain 
dormant,  but  is  now  brought  out  by  some  unknown 
cause.  This  phenomenon  is  called  atavism  and  the 
plant  is  called  an  atavist  (see  p.  420).  If  the  seeds 
of  such  a  plant  are  sown,  probably  few  atavists  or 
none  at  all  will  appear  in  the  progeny.  It  is  to  be 
classed  as  a  sudden  variation. 

If,  now,  we  should  find  a  plant  all  of  whose  leaves 
showed  an  increased  number,  say  nine,  and  all  of 
whose  descendants  showed  the  same  number  coming 
perfectly  true  to  seed,  and  kept  this  up  without  any 
need  of  selection,  this  would  constitute  a  mutation.^ 
Such  a  plant  has  not  been  found,  but  Professor  de  Yries 
hopes  it  may  occur,  and  is  continuing  his  propagation 
of  the  Red  Clover  with  this  end  in  view. 

The  example  of  Clover  makes  clear  Professor  de 
Vries'  ideas  as  to  the  kinds  of  variation.  We  have, 
first,  ordinary  fluctuating  variation  (due  partly  or 
wholly  to  differences  in  nutrition  caused  by  external 
conditions):  second,  sudden  variations,  e.  g.,  mon- 
strosity, atavism,  etc.  (due  to  causes  wholly  unknown) ; 
if  these  should  come  true  to  seed  they  would  be  called 
mutations,  otherwise  not.  A  mutation  is  a  sudden 
variation  which  comes  true  to  seed,  and   he  believes 

1  This  would  constitute  an  extreme  case.  The  mutation  might,  and 
probablj'  would  show  fluctuating  variation  in  the  leaf  numbers,  so  that 
not  every  leaf  would  be  a  nine -leaf  but  the  type  would  be  (for  explana- 
tion of  type  see  page  420),  and  this  type  would  remain  absolutely  constant 
without   selection. 


MAKING    NEW    KINDS    OF    PLANTS  451 

that  this  alone  can  give  rise  to  a  new  species.  Further- 
more, he  includes  in  mutation  the  effects  of  crossing: 
he  believes  that  new  species  can  arise  from  hybridiza- 
tion and  that  there  are  well-established  instances  of 
this. 

Professor  de  Vries  does  not  deny  the  great  value  of 
selection  for  cultivated  plants:  he  merely  insists  that 
the  effect  of  selection  is  only  temporary  and  soon 
ceases  when  selection  stops.  Each  year  the  seedsman 
must  carefully  go  through  his  beds  and  "rogue,"  i.  e., 
remove  the  rogues  or  plants  which  do  not  come  true 
to  seed  or  which  in  any  way  fall  short  of  the  standard: 
only  so  can  he  keep  the  seed  at  all  pure  and  true 
to  type.  And  this  is  the  best  proof  that  he  has  not 
succeeded  by  selection  in  making  a  true  species. 
Where  he  does  get  a  constant  form,  Professor  de  Vries 
believes  it  is  due  to  the  selection  of  mutations  which 
the  seedsman  does  not  distinguish  from  fluctuating 
variations.  He  believes  that  our  garden  varieties  have 
mostly  originated  in  this  way,  since  he  finds  that  most 
of  those  with  which  he  has  experimented  are  constant. 
The  reason  why  they  are  not  regarded  as  such  is  that 
they  are  usually  grown  side  by  side  with  the  parent 
forms  (or  other  nearly  allied  forms),  so  that  crossing 
takes  place  and  hybrid  seeds  are  produced:  these,  when 
sown,  give  variable  forms  after  the  manner  of  hybrids, 
and  much  confusion  results.  His  experience  is  that 
if    a  pure    (i.   e.,    not   crossed)    white    variety    of    a 


452  EXPERIMENTS    WITH   PLANTS 

normally  colored  flower  be  pollinated  from  its  own 
flowers  it  will  produce  white  flowers  only  and  prove 
constant.  Such  varieties,  he  considers,  are  really 
species. 

Every  one  who  has  opportunity  should  be  on  the 
lookout  for  sudden  variations,  both  in  garden  and 
field.  Should  one  be  found  it  should  be  kept  under 
observation,  protected  from  crossing  by  paper  bags 
(as  described  on  p.  289),  and  hand- pollinated.  The 
seed  should  be  saved  and  sown,  in  order  to  see 
whether  it  proves  constant. 

Professor  de  Vries  offers  a  satisfactory  reply  to 
the  opponents  of  evolution,  who  contend,  first,  that 
species  are  constant  and,  second,  that  if  evolution 
were  going  on  we  should  be  able  to  see  the  process. 
He  says  that  species  are  constant  except  at  mutation 
periods:  moreover,  evolution  is  going  on  and  he  has 
seen  it,  not  once  merely,  but  year  after  year  in  his 
garden:  he  has  furnished  seed  to  other  botanic  gardens 
in  various  parts  of  the  world,  and  the  same  phenomena 
have  been  observed.  The  seed  sown  at  the  University 
of  California  produced  about  8  per  cent  of  mutations, 
which  I  have  had  the  privilege  of  personally  observing. 
Further,  his  theory  makes  it  unnecessary  to  seek  for  a 
continuous  series  of  "missing  links,"  since  it  assumes 
that  they  never  existed  in  such  a  series.  His  dis- 
coveries demonstrate  conclusively  that  evolution  can  be 
studied   experimentally  in  a  manner  hitherto   unsus- 


MAKING    NEW    KINDS    OF    PLANTS  453 

pected,  and  furthermore  raise  the  important  question 
whether  we  can  control  evolution  and  so  produce 
species  at  will.  Some  experiments  already  made  in 
this  direction  are  very  encouraging  and  open  up  a 
promising  field  of  research.^ 

1  In  regard  to  the  work  of  Professor  de  Vries,  consult:  de  Vries,  "On  the 
Origin  of  Species,"  Popular  Science  Monthty,  April,  1903;  "My  Primrose 
Experiments,"  Independent,  Sept.  25,  1902;  "On  Hybridization,"  in  Bailey's 
"Plant- Breeding"  third  edition,  1904,  p.  189.  Also  Hubrecht,  "Hugo  de  Vries' 
Theory  of  Mutations,"  Popular  Science  Monthly,  July,  1904;  MacDougal: 
"Professor  de  Vries'  Experiments  on  the  Origin  of  Species,"  Independent, 
Sept.  25,  1902;  Lyle,  "Plant -Making  in  a  Dutch  Garden,"  Everybody's 
Magazine  for  June,  1902;  MacDougal:  "Mutation  in  Plants,"  American 
Naturalist  for   1903. 


INDEX 

Asterisk  (*)  denotes  illustrations 


Abnormality,  420,  421,  449.* 
Absorption,  due  to  osmosis,  17,  60,  (i^,  64, 
67,  122-124. 
of  ammonia  by  soil,  145,  147. 

—  carbon  dioxide,  191,*  192.*  194.  195,  200, 

202. 

—  endosperm,  57,*  179,  180.* 

—  light  by  leaf,  196,  201. 

—  nitrogen    by    plants,    147,    149,     383, 

384. 
soil,  145,  147-150,  383,  384. 

—  organic  substance  from  soil,  150. 

—  oxygen,  .33,  34,*  35,  175,  194,  195,  200, 

287,  317,  388,  390. 

—  phosphorus  by  soil,  145. 

—  potash  bj'  soil,  145. 

—  salts  by  plant,  136,  137,  161. 

—  stored   food,   57.*   164,    179,  180,*   183, 

260.  287.  313. 

—  water  by  root,  88,  102,  103,  119,*  120*- 

123.* 

—  —  —  —  affected  by  temperature,  332. 
seeds,  6,*  7,*  8,*  9*-15,*  10-19,* 

20.*  21,*  22,*  23,*  20,*  27.* 

soil.  111-114. 

wood,  68. 

—  —  affected    by  dissolved    substances, 

18,  124.  217,  336. 

force  required  for, 121-123,*  124. 

Acacia,  protection  of,  against  drying,  217. 

seeds  of.  boiling  to  hasten  germination. 
25. 

sleep  position  of  leaf  of,  218.* 

wood  of,  230. 
Acanthus,  protection  of  pollen  by,  294. 
Acid,  excreted  by  roots,  141-143,*  144,  145. 

in  fruits,  315. 

—  soil,  141,  143,  145.  146. 


Acid,  acetic,  manufacture  of,  387. 
boraeic,  as  preservative,  380. 
carbonic,  as  plant-food,  139. 

—  as  solvent  of  plant-food,  139-145. 

—  given  off  by  root,  141,  142,  143.*  144. 

—  source  of,  in  soil,  141. 

—  See,  also,  Cai-bon  Dioxide, 
carbolic,  as  disinfectant,  364. 
fatty,  171. 

hydrochloric,  155,  157. 
lactic,  378-379. 

nitric,  as  plant-food,  139,  140.* 

—  for  isolating  wood  cells,  235. 

—  test  for  proteids,  165. 

oxalic,  a  by-product  in  proteid  formation 

254. 
phosphoric,  as  plant-food,  139,  140.* 
salicylic,  as  preservative,  3S6. 
sulphuric,  as  plant-food,  139,  140. 

—  in   manufacture   of  superphosphates, 

1.50. 

—  as  test  for  formalin,  377. 
proteids,  166,  178. 

Acer.     See  Maple. 

Aconitum.     See  Monkshood. 

Adaptation.  326-361. 

.Ecidiospores,  403.* 

Aerotropism,  89,  98,  135,  293. 

.(Esculus.     See  Buckeye  and  Horse  Ohest 

nut. 
Estivation,  pi-otection  against  drying  by 

213. 
Agave.     See  Century  Plant. 
Ailanthus,  leaf  scar  of,  212. 
Air  affects  direction  of  growth  of  i)ollen- 

tube,  293. 
affects  direction  of  growth  of  root.  89, 

98.  135. 


;455) 


456 


INDEX 


Air,  apparatus  for  supplying  to  aquaria, 
283,*  285.* 
in  fruit,  317. 

—  leaf,  187-191,  198,*  199,*  200. 

—  seed,  8,*  32,  33,*  34,*  35. 

.    —  -  -  how  absorbed,  30,*  31,  32. 

—  stem,    how  absorbed,    258,   278,   279,* 

280.*  281,*  282. 

—  soil,  36,  37,*  38,  39,*  40,  103,  119,*  120,* 

124,  125,  128,  130,  132. 
amount  best  suited  to  plants,  130. 

—  —  promotes  beneficial  chemical 

changes,  125,  126,  145,  146. 

—  water,  283. 

kept  from  roots  by  flooding,  125. 

sidewalks,  126. 

soil  crust,  125. 

stem  hy  coatings  of  tar,  281. 

kills  bacteria,  382. 
method  of  excluding,  5.* 

saturating  with  water  vapor,  26,* 

27  * 

lack  of,  effect  on  plant,  281,*  282. 
needed  by  fruit,  317. 

leaf,  191,*  192,*  193,*  194,  195. 

plants,  326. 

roots,  125,  126. 

seed,  5.*  6,  32,  33.*  34,*  35,  36,  37,* 

38,  39,*  40. 

—  for  starch  formation,  191. 
nitrogen  of,  used  by  plant,  149,  383-385. 

—  taken  from,  by  bacteria,  383-385. 
plant-food   in,    139,    191,*  192,*  193,*   194, 

195. 

"restored"  by  leaves,  191,*  192,  194,  195. 

trapped  by  pits  of  wood-cells,  235. 

"vitiated"  by  combustion,   191,*  192,  194. 

animals  and  plants,  194,  195. 

— .     See  Respiration. 

water  vapor  of,  absorbed  by  seed,  26,*  27.* 

wood,  68. 

See,  also.  Carbon  Dioxide,  Oxygen,  and 
Nitrogen. 
Air-pump,  187,*  188,*  189,  190,  353. 
Air-spaces,  effect  of  light  on,  345. 

larger  in  water  plants,  339. 
Albumin.     See  Proteid. 
Alcanna,  as  test  for  fats  and  oils,  2.59. . 
Alcohol  and  lye  for  bleaching,  225. 


Alcohol,  coagulates  proteid,  254. 

dissolves  chlorophyll,  181,  254. 

produced  by  yeast, 169,  390. 

use  of,  as  mounting  medium,  .392. 
Alder,  in  northern  latitudes,  356. 

leaf-scars  of,  245. 

protection  of,  against  drying,  214. 
Alfalfa,  killed  by  flooding,  125. 

roots  of,  penetrate  deeply,  134. 
Alinit,  384. 

Alisma.     See  Water  Plantain. 
Alkali,  black,  159. 

for  softening  water,  151. 

renders  absorption  difficult,  336. 

salts  of,  form  crust,  127,  159. 

tolerated  by  some  crops,  350. 

white,  159. 
Alkali  soils,  127,  157-160. 

—  reclamation  of,  159,  160. 

—  salts  found  in,  159. 

—  tests  for,  157,  158. 
Allium.     See  Onion. 
Alluvial  fans.  111. 

Almond,  cover  of,  retains  water,  29. 

escape  of,  from  seed-cover,  54. 
Alnus.     See  Alder. 
Alpine  plants.     See  Plants,  Alpine. 
Althaea.   See  Hollyhock. 
Altona,  cholera  epidemic  of,  372,  373.* 
Alumina,  as  constituent  of  clay,  145. 

fixes  plant-food,  145,  147. 
Amaryllis,  stoma  of,  210. 
Amelanchier.     See  Service  Berry. 
American  Grapes,  protection  of  roots  of,  162. 

Plum.     See  Plum.  American. 
Ammonia,  as  reagent,  156. 

fixed  by  clay,  145,  147. 

produced  by  bacteria,  147,  149,  383. 

test  for  proteids,  165. 
Ammonium  molybdate,  1,56. 

oxalate,  157. 

sulphate,  action  of  plant  on,  161. 
Ampelopsis.     See  Ivy,  Boston. 
Amsterdam,  University  of,  443. 
Anagallis.  See  Poor-man's  Weather-Glass. 
Ananassa.     See  Pineapple. 
Anchusa,  Rust  of,  405. 
Anemone,  protection  of  pollen  by,  295. 

stomata  of,  196. 


INDEX 


457 


Animals,  aid  in  soil  formation,  109. 

avoid  poisonous  plants,  222. 

bury  seeds,  69. 

combustion  in,  35. 

decay  of,  381. 

digestion  in,  166-172. 

distribute  seeds,  323-325. 

food  needed  by,  16-1,  176. 

give  off  carbon  dioxide,  35. 

how  supplied  with  oxygen,  176. 

protection  against.     See  Protection. 

respii-ation  of,  35. 
Annual  rings,  247. 
Annuals,  seed  formation  of,  314. 
Annular  tracheids,  227,*  229,  230,  231.* 
Anthers,  288.* 

opening  of,  289. 

transformed  into  leaf-like  bodies,  359. 

withering  of,  289. 
Antibacterial  substances,  379. 
Anticlines,  111. 
Antipodal  cells,  291.* 
Antirrhinum.     See  Snapdragon. 
Antiseptics,  364. 
Antitoxins,  378,  379. 
Ants  bury  seeds,  69. 
Apium.     See  Celerj'. 
Apple,  effect  of  fertilization  of,  309. 

epidermis  of  fruit  of,  317. 

seed  of  distributed  by  birds,  325. 

stomata  of  fruit  of,  317. 
Apple  Plum.     See  Plum.  Apple. 
Apricot  crossed  with  Plum,  415.* 
Aquaria,  balanced,  194. 

method  of  supplying  air  to,  283*, 

—  —  —  carbon  dioxide  to,  284,*  285.* 
Arabs  preserve  Date  pollen,  294. 
Arachis.     See  Peanut. 
Arid  regions,  richness  of  soil  of,  146. 
Aristotle  on  the  Fig.  310. 
Arrowhead,  337,*  338,*  342. 

air  passages  of,  282. 
Artemisia.     See  Wormwood. 
Arteries,  176. 
Ascent  of   sap,   224,*  225,*   226,   227*-2:il,* 

232*-236,*  237,*  239,  240*-243,  258. 
Asexual  reproduction  liy  spores,  302,*  305, 
393,  394,*  395*  396,*  397.*  398,*  399,* 
401.  402,*  *03.*  404.* 


Asexual  reproduction  by  vegetative  parts, 

433. 
Ash,  leaf-scar  of.  212. 

wood  of.  230. 
Ash  of  plants,  137. 
Ashes  as  fertilizer,  152,  153,  154. 

benefit  puddled  soils,  129. 
Asparagus,  bleaching  of.  34^5. 

tolerates  salt,  350. 
Aster,  cross-pollination  of,  304, 

green  flowers  of,  349. 
Atavism,  420,  449.* 
Atriplex.  .  See  Salt  Bush. 
Attachment  of  plant  to  soil,  87. 

—  root -hairs  to  soil -particles,  119,* 

120,*  121. 
Attraction  of  salts,  etc.,  for  water,  8.  124. 

217,  336. 
Atwater  on  foods,  173. 
Australia,  Rusts  in,  404. 
Autumnal  coloration.  332. 
Avena.     See  Oat. 

Bacteria,  361-389. 
air-hating,  374,  375, 
air-loving,  374,  375. 
behaviour  of  in  cultures.  368. 
cannot  live  in  plants.  378. 
classification  of,  368. 
cultivation   of,   361-365,*  366,  368-370. 

374-375.* 
denitrifying,  383. 
disinfectants  for.  364. 
effect  of  air  on,  382,  383. 

heat  on.  363,  364. 

light  on,  304,  382. 

forms  of,  361,  362.* 
immortality  of,  368. 
nitrifying,  383-384. 
of  air,  366,  367. 

—  "bloody  bread,"  368. 

—  cholera,  371.  372,  373,*  376. 

—  of  decay.  381-387. 

—  diphtheria.  376. 

—  hay,  361-365. 

—  lockjaw,  362,*  378. 

—  milk,  372-378,  381. 

—  root  tubercles,  384.  385. 

—  scarlet  fever,  376. 


458 


INDEX 


Bacteria  of  tuberculosis,  376. 

—  typhoid,  371,376. 

—  vinegar,  387. 

—  water,  368. 
parasitic,  380. 

prepare  nitrogen  for  the  plant,  149,* 
150,  383. 

propagation  of,  362,*  371. 

pure  cultures  of,  367-368. 

respiration  of,  374. 

saprophytic,  380. 

spores  of,  362,*  365. 
Bagley,  acknowledgement  to,  x. 
Bailey  on  agriculture,  109,  129,  133,  15^. 

—  gardening.  249,  263. 

—  plant-breeding,  409,   420,  421,  428, 

441,  453. 

—  pruning,  264. 

—  study  of  branches,  245. 
Balance,  method  of  making,  13.*  14.* 
Bamboo,  protection  of  stomata  by,  214. 
Barberry,  protection  of,  against  animals. 

222. 

Rust  of,  402,  403,*  404.* 
Bark,  262,*  279. 

binds  stem,  248. 

formation  of,  256. 

function  of,  256,  333. 

protects  against  drying,  333. 

slitting  of,  to  prevent  binding,  248. 

softened  to  prevent  binding,  248. 

stretching  of,  247. 
Barley,  pepsin  in,  172. 

roots  of,  explore  soil  thoroughly,  133. 

Rust  of.  404. 

seeds  of,  germinate  while  immature,  43, 

Smut  of,  4U0-401. 
Bartlett  Plum.     See  Plum,  Bartlett. 
Barium  hydrate,  158. 
Bast,  120,*  198,*  199,*  224,*  225,  226,  227,* 

231,*  232,*  233,  236,*  254-257. 
Bast-ring,  226,  246. 
Beach  Plum.     See  Plum,  Beach. 
Beals  on  soil,  133. 
Beam,  effect  of  strains  on,  265. 
Bean,  77,*  141,  144. 

food  in,  177. 

get'ing  above  ground  of,  71,*  76,  77. 

path  of  water  in  the  seed  of,  8,*  23. 


Bean,  pocket  of  seed  of,  20.* 

root  tubercles  of,  149. 
Bean.     See  also  Horse  bean. 
Bean,  Cranberry,  hybrids  of,  428. 
Bean,  Horticultural  Pole,  hybrids  of,  428. 
Bean,  Lima,  absorption  of  water  by,  7. 

—  germination  of,  81,  85. 

—  resting  period  of,  43. 

—  twining  of,  275. 

Bean,  Pink,  germination  of,  51. 

Bean,  Pole,  twining  of,  275. 

Bean,  String,  twining  of,  275. 

Bean  hybrids,  428. 

Beech,  hairy  covering  of  young  leaf  of,  213. 

—  sun-  and  shade-leaves  of,  345.* 
Beer,  manufacture  of,  169,  391. 

Bees,  partial  to  certain  colors,  298,  299. 

—  power  of  scent  of,  300. 

—  visit  but  one  kind  of  flower  at  a  time, 

299. 

—  visual  powers  of,  300. 
Beet,  sugar  in,  122. 

self-  vs.  cross-pollination  of,  302. 
Beet,  Sugar,  tolerates  alkali,  350,  440. 
Beggar's-ticks,  dispersal  of  seed  of,  324.* 
Begonia,  332. 

root  pressure  of,  243. 

transpiration  of,  204. 
Bending  stem  to  increase  fruit  production. 

318. 
Benzine,  test  for  fats  and  oils,  165. 
Berberis.     See  Barberry. 
Bertholetia.     See  Brazil  Nut. 
Berries,  pulp  of,  retains  water,  29. 
Bessey,  on  plant-breeding,  441. 
Beta.     See  Beet. 
Betula.     See  Birch. 
Bichromate  of  potassium.     See  Potassium 

bichromate. 
Biennials,  flowering  of,  286. 

seed  formation  of,  314. 
Bindweed,  calyx  of,  288. 

twining  of,  275. 
Birch,  contains  fat  in  winter,  259. 

dispersal  of  seeds  of,  321. 

in  northern  latitudes,  356. 

protection  of,  against  drying,  214. 

lenticels  of,  278. 

run  of  sap  of,  in  spring,  259. 


INDEX 


459 


Birds  bury  seeds,  69. 

distribute  seeds,  324,  325. 
Bird's-eye  Maple,  262. 
Bitter  taste  as  protection  against  animals, 

222    223 
Blackberi-y,  climbing  of,  270. 

contraction  of  root  of,  87. 

protection  of  stomata  by,  214. 

rooting  at  tip  of,  87. 
Blackberry  hybrids,  426,*  427.* 
Bleaching  powder,  23. 
Bleeding  of  plants,  243.* 
Blood,  coagulation  of,  171. 

composition  of,  171. 

in  relation  to  oxygen,  176. 
Blue,  preferred  by  bees,  298,  299. 
Blue  rays  cut  out  by  potassium  bichromate, 

265. 
Blue  jays  bury  seeds,  69. 
Bluestone.     See  Copper  Sulphate. 
Blue  Vitriol.     See  Copper  Sulphate. 
Boilers,  pressure  in,  74. 
Boiler-scale,  151, 
Bone  as  fertilizer,  150,  151.  153. 

phosphorus  from,  150. 
Bone-black  as  fertilizer,  151. 
Bone-meal  as  fertilizer,  151. 
Bone-superphosphate,  139,  150,  153,  154. 
Boneset,  protection  of,  against  animals,  223. 
Boracic  acid.     See  Acid,  Boracic. 
Bordeaux  mixture,  407. 
Bordered  pits,  227,*  232,*  234.* 
Borers,  may  promote  fruit  production,  319. 
Boston  Ivy.     See  Ivy,  Japanese. 
Bran.  178. 
Branch.    See  Stem. 
Brassica.     See  Brussels  Sprouts,  Cabbage, 

Mustard  and  Rape. 
Brazil  nut,  micropyle  of,  8,*  9. 
Bread,  178. 

crust  of,  contains  dextrin.  168. 

Mould.     See  Mould. 
Breaking  stem  to  increase  fruit  production, 

318,  319. 
Briggs,  on  soil,  129,  133. 
Brine,  as  preservative,  386,  387. 
Broom,  protection  of,  against  drying,  215. 
Brownian  motion,  361. 
Brussels  Sprouts,  bud  of,  250,*  251. 


Buckeye,  flower-buds  of,  286. 

fruit  of,  how  supplied  with  food,  313. 

germination  of,  58,*  59,*  60,*  85. 

pocket  of  seed  of.  20,  58.* 

preparation  for  flowering  of,  286. 

seed-cover  of.  8. 

seed  of,  structure  of,  58,*  59,*  60. 

See,  also.  Horse-chestnut. 
Buckwheat,  germination,  47. 

self-  vs.  cross-pollination,  302. 
Buds,  crystals  in,  254. 

flowers  of,  286-288. 

food  in,  253. 

formed  on  roots,  249. 

latent,  262.* 

opening  of,  25 1. 

protection  of,  against  dryness,  213,  214. 
251,  334. 

structure  of,  250,*  251. 
Bud-scale,  288. 

function  of,  214,  251. 
Bud  variation.     See  Variation. 
Bulbs,  propagation  by,  433. 

storage  of  food  in,  260,  261,  286. 
Bulrush,  strengthening  fibers  of,  267.* 
Bundles.     See  Fibrous  Bundles. 
Bur  Clover.    See  Clover,  Bur. 
Burbank,  acknowledgement  to,    x,    409. 

work   of.   409-411,*  412,   413,*  414*   415,* 
416,*  417,  422,   423,*  424,*  425,*  426,* 
427,*  428.  429* -432. 
Burdock,  dispersal  of  seeds,  323.* 
Burs,  323.* 
Butter,  emulsification  of,  169,  170. 

preservation  of,  386. 
Buttercup,  contraction  of  root  of,  87. 

water,  338,  339.* 
Butterflies,  visual  powers  of,  300. 

Cabbage,  self-  vs.  cross-pollination  of,  302. 

strengthening  fibers  of  leaf  of,  267. 
Cactus,   effect  of  water  and  darkness  on, 
329,*  SrO.  331.* 

fruit  of,  production  of,  increased  by  dry- 
ness, 342. 

habit  of.  329,  330,  331.* 

protection  of,  against  animals,  334. 

dryness,  215,  333. 

storage  of  food  in,  286. 


460 


INDEX 


Cactus,  storage  of  water  in.  334. 

soil  needed  by,  108. 
California,  University  of,  445,*  452. 
Callitriche,  air-spaces,  333.* 
Callus,  249,  263. 
Calorie  defined,  174. 
Calyx,  288.* 

work  of,  287,  288. 
Cambium,  227,*  232,*  236.*  246-248. 
Cambium-ring,  246. 
Canada,  forests  of,  356. 
Canal  banks  protected  by  plants,  277. 
Cane,  Sugar,  protection  of,  against  drying, 

333,  334.* 
Cane-sugar,  165. 

Canna,  protection  of,  against  drying,  213. 
Canna  hybrids,  428. 
Canning,  386. 

Capillary  action  of  soil,  116. 
Caprification  of  Fig,  310,  311. 
Carbohydrates.     See  Starch  and  Sugar. 
Carbon,  energy  from,  173. 
Carbon  dioxide,  absorption  of.  by  chloro- 
phyll, 202. 

leaf,  200. 

—  apparatus  for  supplying  to  aquaria, 

283,*  284,*  285.* 

—  as  constituent  of  starch,  186. 

—  as  measure  of  energy  set  free,  174, 
-—  as  plant-food,  139. 

—  decomposed   by  leaf.  191,*  192,*  193,* 

194,  195. 

—  generation  of,  284.* 

—  in  air,  187,  194. 

—  measurement  of,  34,*  175. 

—  produced  by  leaves,  194,  195. 

Moulds,  394. 

root.  141,  142,  143,*  144. 

seeds,  6,  33,  34,*  35, 

Yeast,  390. 

—  role  of,  in  respiration.  175. 

—  supply  of,  affects   starch  formation, 

193.* 

—  unites  with  water  to  form  starch,  187, 

193,  202. 
See,  also.  Acid,  Carbonic,  and  Respiration. 
Carbonate  of  lime.    See  Lime  carbonate. 
Carbonic  acid.   See  Acid,  Carbonic. 
Carex.    See  Sedge. 


Carrot,  contraction  of  root,  87. 
for  artificial  root-hair,  122. 
storage  of  food  in,  260,  313. 
sugar  in,  122. 
Caruncle,  2. 

function  of,  29. 
Carya.    See  Hickory,  Pecan. 
Casein,  172,  377. 
Castanea.    See  Chestnut. 
Castor-bean,  1,  2.* 
absorption  of  water  by,  7,  29. 
air  reservoir  of  seed  of,  42. 
cross-pollination  of,  302. 
caruncle  of.  retains  water,  29. 
endosperm  of,  function  of,  179. 
getting  above  ground  of,  72.* 
lipase  in,  170,  171. 
micropyle  of,  9. 
protection  of  pollen  by,  295. 
resting  period  of  seed  of.  44. 
seed-cover  of,  8. 
seed  of,  structure  of,  29. 
seed  leaf  of,    function   of,  178,  179.  185 

186.* 
self-  vs.  cross-pollination  of.  302. 
Caulicle.  1,*  2,*  3.*  4.* 
direction  of  growth  of,  59. 
pocket  around,  20,*  58.* 
Celery,  bleaching  of,  346. 
Cell,  antipodal,  291.* 
bast-,  120,*  198,*  199,*  224,*  225,  226,  227,* 

231,*  232,*  233,  236,*  254-257. 
cambium,  227,*  231,*  232,*  236,*  246-248. 
chlorophyll  granules  in,  198.*  199,*  200, 

201,*  2C2. 
collenchyma,  268.* 
crystals  in.  232,*  254. 
division  of,  227,*  232,*  236,*  246.  362.*  371. 

390.* 
egg-,  290,  291.* 
epidermal,    198,*    199,*  334,*   335,*  336,* 

337,*  338,*  340,*  .344,*  345.* 
guard-,  198,*   199,*   200,   208,*  209,*  210,* 

211.*  336,*  337,*  340,*  344,*  345.* 
hair-,  324,*  335,*  337.* 
in  relation  to  growth,  64,  65,*  66-68. 
isolation  of,  235. 

nucleus  of,  65,*  66,  290,  291,*  311. 
osmosis  in,  64.  123,  124,  208,  209. 


I 


INDEX 


461 


Cell  parenchyma,  of  leaf.  198.*  199*-202.* 
337,*  338,*  344,*  345.* 

seed,  65.*  66. 

stem.   227,*    231,*    232,*   233,    236,* 

257.  258,  328,  333.* 
root,  120,*  121. 

pits  in  wall  of,  227,*  229.  232.*  233,  234,* 

235. 
protoplasm  of,  65,*  66,  290,  291.* 
sclerenchyma,  224,*  225.*  2J7,*  231,*  232,* 

236,*  266.  267,*  268. 
starch  in.  See  Starch, 
strengthening,  224,*  225,*  227,*  231,*  232,* 

236,*  266,  267,*  268. 
structure  of,  65,*  66. 
water  in,  64,  123,  124,  208,  209. 
wood-,    120,*   121,   198,*    199,*    224*-227,* 
228-231,*  232*-234,*  235.  236*-237,  238*- 
240,*  341. 
Cell-wall,  64,  65,*  66. 
Cellular  structure.     See  Histology. 
Cellulose,  65,*  66. 

decomposition  of,  381. 
Centrifugal  force,  effect  of,  on  direction  of 
growth  of  stem  and  root,  92,  93,*  94. 
Century     Plant,     protection     of,    against 
animals,  222,  334. 

—  protection  of,  against  drying  by  epider- 

mis. 333. 

—  seed  formation  of,  314. 

—  storage  of  food  in,  260,  286. 

—  storage  of  water  in.  334,  335. 
Ceratophyllum.     See  Hornwort. 
Cereals  in  crop  rotation,  160. 
Charcoal,  372. 

Checkerberry.     See  Partridge-berry. 
Cheese,  377.  j 

Chemical  action  due  to  light,  182,*  184,*  185,    ' 
195,  196.  201,  316.  364,  382.  | 

—  in  the  plant,  166-177,  182-196,  253,  254, 

258,  259,  314-316. 

soil,  125,  139-15'J. 

soil-formation,  109. 

— .     See,  also.  Respiration. 

Chemotropism,  293,  294. 
Cherry,  evergreen,  415. 

flavor  of,  288.* 

lenticels  of,  278. 

protection  of,  against  drying,  214. 


Cherry,  seeds  of.  distributed  by  birds.  325. 
Chestnut,  on  poisonous  plants,  222. 
Chestnut,  leaf  mosaic  of,  219.* 

protection  of  fruit  of.  320. 

wood  of,  230. 
Chicfcgo,  sewage  of,  382. 
Chickory,  flowers  of,  attract  bees,  299. 

protection  of  root  of,  162. 
Chili  saltpeter.     See  Sodium  nitrate. 
Chloride  of  lime.     See  Lime  chloride. 
Chloroform  in  testing  for  fats  and  oils, 

165. 
Chlorophyll  absorbs  carbon  dioxide,  202. 

cannot  form  in  cold  weather,  354. 

—  darkness.  185. 

decomposition    of.    causes    autumnal 
colors,  332. 

effect  of  light  on.  184,*  185. 

function  of,  185,  201. 

in  stem.  278. 
Chlorophyll -granules,  198,*  199,*  200,  201, 

202.* 
Cholera,  371-373,*  376,  380. 
Chrysanthemum,  sports  of,  420. 
Cichorium.     See  Chickory. 
Cinnabar,  injection  of  wood  with,  237. 
Cinque  foil,  hairy  covering  of  leaf.  213,  334. 

protection  of,  against  drying,  334. 

protection  of,  against  animals,  223. 
Cistus,  protection  from  drying,  .334. 
Clay,  burning  of,  106. 

burned,  benefits  puddled  soils,  129. 

composition  of,  i06,  107. 

fixes  ammonia,  145,  147. 

—  dung  liquor,  145. 

—  plant-foods,  145. 
flocculated  by  lime,  152. 

is  impervious  to  water,  125. 

lifts  water  higlier  than  sand  does.  118. 

microscopical  examination  of,  106. 

percolation  in,  113. 

plant-food  in,  106. 

properties  of,  106. 

richer  in  plant-food  than  sand  is,  146. 

size  of  particles  of,  106. 

water-holding  capacity  of,  132. 
C'lay  loam,  108. 
Clematis,  climbing  of,  270,  271.* 

dispersal  of  seeds  of,  .vl2.* 


462 


INDEX 


Climbing  plants.  270,  271.*  272.  273,*  274, 

275.* 
Clock,  floral.  295. 

Clotbur,  dispersal  of  seeds  of,  324.* 
Clover,  benefited  by  lime,  151.* 

in  crop  rotation.  160. 

leaves  of,  follow  sun,  218. 

position  of  flowers  of,  307. 

root  tubercle  of.  149.* 

sleep  position  of,  218. 
Clover,  Bur,  dispersal  of  seed  of.  324.* 

Red.  variation  in,  448.*  449*-  450.* 
Cobffia,  calyx  of,  288. 

Cobalt    chloride,    as    index    of    transpira- 
tion. 203. 
Cockle  -  bur.    resting    period    of    seed    of, 

44. 
Cocoanut,  distribution  of,  by  water,  325. 

endosperm  of.  function  of,  57,  179,  180. 

germination  of,  .56,  57,*  58. 

structure  of  fruit  of.  56.  57,*  58. 
Cocoanut  oil.    See  Oil,  cocoanut. 
Cocos.    See  Cocoanut. 
Cohn's  solution,  formula  for,  398. 
Cold.    See  Heat. 
Collenchyma,  268.* 
Colon  bacillus.  371. 
Color  of  autumn  leaves,  332. 

—  flowers,  297-300. 

—  fruits,  316,  325 

—  fruits   and  flowers  affected  by  light, 

347. 

—  night-blooming  flowers,  300. 
preferred  by  insects,  298,  299, 

Color-contrast  in  flowers,  297,  298. 
Combustion,  35. 

as  source  of  energy,  173. 

brought  about  by  ferments,  173. 
Companion  cells.  227.*  231.*  232,*  255. 
Comnass  plants,  346. 

Composite    family,    cross  -  pollination    of, 
303.* 

—  green  flowers  of.  349. 
Composition  of  soil,  103-109. 

—  starch,  186,*  187. 
Compost,  147.  148. 
Conditions  of  growth,  252,  253. 
Conduction.    See  Stem,  path  of  air,  etc.,  in. 
Conidia,  399,  402,  403, 


Conifers,  humus    of.    preferred    by    som* 
plants,  351. 

pollen  of,  carried  by  wind,  300. 

See,  also.  Pine. 
Conn,  on  bacteria,  408. 
Contagious  diseases,  380. 
Contact-bed  for  sewage,  382. 
Contraction  of  root,  87. 

—  wood,  68. 
Convolvulus.    See  Bindweed. 
Copper  sulphate,  161. 

as  a  disinfectant,  364,  400,  401. 
Coreopsis,  cross-pollination  of.  304. 
Cork,  232,*  236,*  256.  279. 

protects  against  drying,  333. 
Cork-cambium.  232,*  236.* 
Corms,  propagation  by.  433. 

storage  of  food  in.  260,  261. 
Corn,  bran  of,  437. 

breeding  of,  355,  434-441. 

canning  of,  386. 

cross-pollination  of.  302. 

endosperm  of,  3,*  179. 

fat  in.  437. 

fibrous  bundles  of,  225.*  226,*  230,  231.* 

food  in.  3,*  437. 

germ  of,  3,*  437. 

germination  of,  21.  22.*  47.  71.*  72. 

getting  above  ground  of,  71.* 

in  silo,  388. 

leaf-scar  of,  212. 

oil  of,  437. 

original  home  of.  440. 

pepsin  in,  172. 

pollen  of,  carried  by  wind,  301.  436. 

protection  of,  against  drying,  213,  334, 

tip  of  stem,  71,*  79. 

proteid  in,  437. 

roots  of,  explore  soil  thoroughly,  133 

strength  of.  268. 

structure  of.  268. 

root  pressure  of.  243. 

seed-leaf  of.  3.*  179. 

self-  vs.  cross-pollination,  302. 

silk  of,  292,  301. 

Smut  of.    See  Smut  of  Corn. 

starch  in,  3.  437. 

stem  of.  structure  of,  225,*  230,  231  * 

rigidity  of.  269. 


INDEX 


463 


Corn,  stigma  of,  292.  301. 

strengthening  fibers  of,  231,*  266 

structure  of  grain  of,  2,  3.* 

wandering  of,  440. 

water  in,  437. 

Xenia  in,  311. 
Corn,  Sugar,  endosperm  of,  3. 

—  seed-leaf  of,  179. 
Corolla.  288.* 
Correlation,  79,*  359.  360. 
Corrosive  sublimate  as  disinfectant,  364. 
Cortex.     See  Rind. 
Corylus.     See  Filbert,  Hazel. 
Cosmos,  cross-pollination,  304. 
Cottonseed  oil.    See  Oil,  Cottonseed. 
Cotyledons.    See  Seed-leaves. 
Cover.     See  Seed  cov*  r. 
Cow  Wheat  loves  mild  humus,  351. 
Cowpox,  379. 

Cracks,  seeds  buried  in,  69. 
Crataegus.  See  Hawthorn. 
Crocus,  opening  and  closing  of  flower  of, 

affected  by  heat,  296. 

storage  of  food  in,  260. 
Crops,  dependence  on  water  supply,  133. 

green,  in  crop  rotation,  160. 

rotation  of,  160,  161. 

white,  in  crop  rotation,  160. 
Cross-pollination,  301,302,  303,*  304,*  305,* 

306.* 
Crossing,  process  of  430.  431,*  432. 

results  of,  411,*  413.*    416,*  422,*    423,* 
424,*  425,*  426,*  427,*  428,  429,*  434. 

species  originate  from,  451. 

utility  of,  421. 
Crude  food.     See  Food,  Crude. 
Crust.     See  Soil  crust. 
Cucumber,  Squirting,  dispersal  of  seed  of, 

321.* 
Cucurbita.     See  Pumpkin  and  Squash. 
Crystals,  232,*  254. 

Cultivation   conserves  soil   moisture,  115,* 
116,*  117,  125,  129,  133. 

should  be  adapted  to  depth  of  root,  135. 
Cupra-ammonia  as  light  filter,  265. 
Currant,  acid  in,  315. 
Curve  of  variation.     See  Variation ,  Curve 

of. 
Cut.  fever  caused  by,  262,  263. 


Cuticle,  197,  198,*  199,*  328.  334.* 

effect  of  light  on,  345. 

of  water  plants,  339. 
Cuttings,  correlation  in,  359. 

fever  in,  262,  263. 

propagation  by,  433. 

regeneration  in,  257. 

soil  required  by.  262.  263. 

transpiration  of.  282. 

treatment  of,  263. 
Cydonia.     See  Quince. 
Cypress,  wood  of.  230. 
Cytisus,  331,  332.* 

protection  of,  from  drying,  by  sunken 
stomata,  215. 

See,  also,  Broom. 

Dahlia,  root  pressure,  243. 

Daily  movements  of  flowers,  295-298. 

leaves,  218.* 

Daisy,  cross-pollination  of,  304. 

European,  422. 

Field,  422,  423.* 

Japanese,  422,  425. 

Ox-eye,  variation  in,  417,  418,*  419.* 

Shasta,  422,  423,*  424.*  425,*  427. 

hybrids,  422,  423,*  424,*  425,*  427. 
Dandelion,  behavior  of  leaf  of,  252. 

dispersal  of  seeds  of,  322,  323. 

effect   of  saturated  atmosphere  on.  341, 
342.* 

flowers  of,  arrangement  of,  298. 

affected  by  light,  298. 

opening  and  closing  of  flowers  of,  affected 
by  light,  295. 

protection  of  pollen  by,  295. 

root  by,  162. 

stalks  of,  tissue  tensions  in,  269,  273.* 
Darkness.    See  Light. 
Darwin,  on  orchid  pollination,  307. 

—  origin  of  species,  441,  442. 

—  self-  vs.  cross-pollination,  301. 

—  soil  formation,  109. 
Date,  germination  of,  180.* 

fruiting  of,  356. 

seed-leaf  of,  180.* 

vitality  of  pollen  of,  294. 
Daucus.    See  Carrot. 
Decay,  381-387. 


464 


INDEX 


Decomposition  due  to  bacteria,  147, 148, 151, 
381-187. 
of  carbon  dioxide  by  leaf,  191.*  192.* 

—  rock  by  chemical  action,  etc.,  144,  145. 

—  starch  by  heat,  86,*  87. 
Deer-berry.    See  Partridge-berry. 
Deformity.  420,  421. 
Delphinium.    See  Larkspur. 
Deutzia,  cross-pollination  of,  303. 
Dew,  formation  of,  117. 

Dextrin,  changed  to  grape  sugar,  168. 

in  bread  crast,  168. 

formation  of,  167,  168. 
Diastase,  166,  167. 
Dicotyledons,  characterized,  226. 
Digestion  in  animals,  166-172. 

—  plants,  166-172. 

Dikes,  protected  by  plants,  277. 

Dioecious  plants,  302. 

Diphtheria,  376,  380. 

Directive  action  of  air,  89,  98,  135,  293. 

—  —  chemical  substances,  293,  294. 
gravity,  88,*  89,*  90,  91,*  92,  93,*  94, 

95,  98,*  99,  264,  277.  308. 

light,  264,  346. 

water,  95,*  96,*  97,  98. 

Diseases  of  plants,  397,  398,*  399,*  400,  401, 
402,*  403,*  404-407,*  408.* 

damage  done  by,  400,  401,  406. 

prevention  of,  400,   401,   407,  408. 

440. 
Disinfectant,  .364. 
Dispersal  of  seeds,  320-325. 
Distilling,  137,*  138. 
Distribution  of  seeds,  320-325. 
Dog's  Mercury,  loves  mild  humus,  351. 
Drought.    See  Dryness  and  Water. 
Drupes,  protection  against  drying  of  seed 

of,  317. 
Drying,  protection  against.    See  Protection 

against  drying. 
Dryness,   effect  of,  on  plant,   82,   211-217. 
326,  327,*  328,*   329*-.331,*   332,*  333,* 
334,*  335,*  336,*  337,*  338,*  339,*  340*- 
342,*  343.* 
See,  also.  Water. 
Ducts,   224,*  226,  227,*  228,  229,  230.  231,* 
232,*  233,  234.* 
length  of,  236.  237.* 


Ducts,  resin-,  235,  236.* 

■water  travels  faster  in,  228,  229,  230,  237. 
Dung  liquor,  fixed  by  clay,  145. 
Dust  clogs  stomata,  215 
Dusty  Miller,  hairy  covering  of,  213. 

—  protection  of,  against  drying,  333. 

water,  214. 

Earliness,  355,  411,  412. 

Earth.    See  Soil. 

Earthworms  bury  seeds,  69. 

Eau  de  Javelle,  23. 

Echinocystis.    See  Cucumber,  Squirting. 

Echium,  Rust  on,  405. 

Egg,    ood  in,  176,  177. 

of  plants,  290. 

presei'vation  of,  387. 
Elaborated  food.    See  Food,  Elaborated. 
Elasticity  of  stem,  269. 
Elder,  flowers  of,  298. 

pith  of,  269. 

stem  of,  268,  269. 
Electric  light,  346. 
Elm,  buds  formed  on  roots  of.  249. 

cross-pollination  of,  303. 
Embryo.    See  Germ  and  Seed. 
Embryo-sac,  290,  291.* 
Endosperm,  2,*  3,*  4,  :u*  179,  180.* 

absorption  of,  57, ^^  179,  180.* 

in  Xenia,  311. 
Endosperm  nucleus.  291,*  311. 
Energy  absoi-bed  from  sunshine,  195,  196, 
201. 

in  foods,  173. 

in  starch,  196. 

uses  of,  173-175. 
Environment,  effect  of.  on  the  plant,  W'H'.- 

360. 
Eosin,  22,  24,  66,  161,  224,  225,  228,  230.  24'J, 

251. 
Eosin  stains,  how  removed,  23. 
Epidermis  of  fruit,  317. 

of  leaf,  197,  198,*  199,*  204,  205,  21!).  2i:{, 
214. 

protects  against  drying,  333,  331.* 
Epilobium,  dispersal  of  seeds,  323. 
Equisetum.     See  Horse-tail. 
Erodium.'     See  Filaree. 
Ether,  test  for  fats  and  oils.  165. 


I 


INDEX 


465 


Etiolation,  184,*  185.  328,*  354.* 
Eucalyptus,  protection  of,  against  di-ying, 

214,  217.  317,  333,  334. 

fruit  of.  320. 

Eupatorium.     See  Boneset. 

European  Plum     See  Plum,  European. 

Evaporation.     See  Soil,  Evaporation  from, 

and  Transpiration. 
Evening  Primrose.  See  Primrose,  Evening. 
Evolution,  330,  441-403. 
control  of,  453. 

indicated  by  variation  curve,  419.'*' 
Excentric  growth,  348-350.* 
Excretions,  nitrogen  in,  176. 

poisonous  character  of,  378. 
Experimental     morphology.      See    Plant, 

form  of. 
Exposure,  effect  of,  on  fruit   production, 

319 
External    agents,    326-361.     See,  also.  Air, 

Food,  Gravity,  Heat,  Light,  Water, 

Wind. 
Eye,  effect  of  light  on,  196. 

Fagopyrum.     See  Buckwheat. 
Fall  wood,  232,*  236.*  247. 
Fascination,  420,  421. 
Fats,  changed  to  starch,  259. 

decomposition  of,  381. 

emulsification  of,  169,  170. 

energy  from,  173. 

formation  of,  170,  201. 

in  eggs, 177. 

—growing  region,  253. 

— seeds,  165,  177. 

—trees,  259. 

saponification  of,  170,  171. 

tests  for,  165,  259. 

See,  also.  Oil. 
Feces  contain  waste  nitrogen,  176. 
Fehling's  solution,  preparation  of.  164,  1()5. 
Feldspar,  106.  107. 
Fermentation  by  bacteria,  380. 

—Yeast,  169. 
Ferments,  166. 

cause  oxidation,  173. 

restore  vitality  of  seeds,  44. 
Fernow,  on  forestry,  245. 
Ferns  as  shade  plants,  344. 


Ferns,  protection  against  drying,  213. 

rhizomes  of,  277. 

soil  needed  by,  108. 

unrolling  of  leaf  of,  252. 
Fertilization,  291,*  292.* 

after  effect  of,  309,  360. 
Fertilizers,  139-160. 

effect  of,  on  fruit,  315. 

fruit  production,  318. 

Fever  caused  by  wounds,  262,  263,  388. 
Fibrin  coagulation  of,  171. 

for  digestion  experiments,  171,  172. 
Fibrous  bundle,  198,*  199,*  224,*  225,*  226. 
227,*  228,  230,  231,*  250,*  251,  317. 

effect  of  water  on,  335.* 
Ficus.    See  Pig,  Rubber  Plant. 
Fig,  flower  structure  of,  310. 

pollination  of,  310,  311. 
Filaree,  seeds  of,  bury  themselves,  70,*  71. 
Filbert,  absorption  of  water  by,  7. 

openings  in  cover  of,  9. 

path  of  water  in  cover  of,  9,  24. 
Filtration  of  water,  372. 
Fire,  protection  against,  by  bark,  256. 
Fish,  preservation  of,  386. 
Fisher,  on  cookery,  178. 
Five-finger.     See  Cinquefoil. 
Flavor,   affected    by    external    conditions. 
318,  319,  342. 

improvement  of,  by  breeding,  413,  415. 
Flax,  absorption  of  water  by,  728. 

seed-cover  of,  holds  water,  28. 
Flesh-forming  foods,  176. 
Fleur-de-lis.    See  Iris. 
Flies  carry  disease,  380. 

prefer  yellow,  299. 
Flinty    texture  protects  against  animals. 

223. 
Floods,  relation  of,  to  forests,  112. 
Floral  clock.     See  Clock,  floral. 
Florida,  forests  of,  356. 
Flour,  proteid  in,  177. 

starch  in,  177. 
Flower,  attraction  of  insects  for,  297-300. 

color-contrasts  in,  298. 

color  of,  affected  by  light,  347. 

double,  produced  by  breeding,  425.* 

effect  of  heat  on,  296,  347. 

light  on,  295-298,  347,  348. 


DD 


466 


INDEX 


FJower,  effect  of  water  on,  496,  342. 

foo.l  needed  by,  286,  287, 

formation  of.  286,  287. 

improvement  of,  by  breeding,  422,  423,* 
424,*  425,*  427. 

injury  of,  288. 

night  blooming,  299,  300. 

opened  by  insects,  308. 

opening  and  closing  of,  296,  297. 

platforms  of,  309. 

production  affected  by  heat,  347. 

light,  347. 

protection  of,  against  drying,  288, 

insects,  308. 

water,  294,  295. 

position  of,  30T,  308. 

respiration  of,  287. 

sets  free  heat,  287. 

structure  of,  288,*  290,  291.* 

work  of,  28G-311. 

See,   also.  Anthers,   Petals,    Ovary  and 
Ovule. 
Flower-buds,  286,  287. 
Flowering,  preparation  for,  286,  287. 
Food,  as  source  of  energy, 173,  176. 

—  material  for  growth,  173. 
crude,  201,  136-162. 
digestion  of,  166-172. 
effect  on  plant,  349-351. 

elaborated,  57^*  65,*  164,  169,  179.  180,* 
183,  253.  254,  260,  278,  286,  287,  313. 
314. 

energy  in,  how  measured,  173. 

flesh-  orming,  176. 

from  the  air.  200. 

—  —  soil,  201. 

how  conveyed  to  fniits,  313. 
in  buds,  253. 

—  eggs.  176,  177. 

—  leaves,  181.  332. 

—  seeds,  57,*  65,*  164-180,*  437. 

—  root,  122.  255,  260. 

—  stem,  169,  243,   250,   253,  254-260,  286, 

287,  313.  314. 

—  soil,  146. 

lack  of.  promotes  fruit  production.  350. 
made  soluble.  166-172. 
manufacture  of.  182-203,  253,  254,  278. 
mineral.  136-162, 


Food,  muscle-forming,  176. 
needed  by  fruits,  312-316. 

plant,  326. 

organic,  absorbed  from  soil,  150. 
preservation  of,  376,  377,  385-388,  397. 
required  for  growth,  253. 
storage  of,  in  preparation  for  flowering, 

260,  286,  287. 
stored,  utilization  of,  57,*  164,  179.  180.* 

183,  260,  286,  287,  313. 
plant,  dissolved  by  carbonic  acid,  139-145. 

—  fixed  by  clay,  145. 
—  humus.  145, 

—  set  fi'ee  by  lime.  152. 

—  raw.  136-162.  201. 

wandering  of,  57.*  164,  169,  180,  183,  253, 
254-257,  259,  260,  286.  287.  313.  314. 
Forage  crops,  time  for  cutting.  314. 
Forests,  effect  of  heat  on,  356. 

hiimus  in.  107. 

prevent  floods.  112. 

remain  naturally  in  good  tilth,  129. 
Forest,  trees  of.  differ  from  isolated  speci- 
mens. 261. 
Form  of  plant, effect  of  external  agents  on. 

See  Plant,  form  of. 
Formalin,  as  disinfectant  and  preservative 
28,  364,  377.  386,  401. 

test  for,  in  milk,  377. 
Foxtail,  seeds  of,  bury  themselves,  71. 
Fragaria.    See  Strawberry. 
Franklin,  on  gypsum  as  fertilizer,  151. 
Fraxinus.    See  Ash. 
Freak,  420,  421.  440.* 
Freezing.    See  Heat. 
French  Prune.    See  Prune.  French. 
Frost.    See  Heat. 
Fruits,  acid  in,  315. 

air  in,  317. 

air  needed  by,  317. 

air,  how  conveyed  to,  317. 

attract  animals.  324,  325, 

benefited  by  ringing,  257. 

effect  of  light  on,  316,  347, 

—  —  water  on,  342. 

wind  on,  349. 

defi'^ition  of,  4,  312. 
fat  in,  314. 
epidermis  of,  317, 


INDEX 


467 


Fniits.  fibrous  bundle  in.  317. 
flavor    of,    increased    by    dryness     and 

warmtli,  315. 
food  needed  by,  312-316. 
improvement  of.   by   breeding,   409-411,* 

412,  413.*  414,*  415,*  416,*  417. 
oil  in,  314. 
path  of  food  to,  313. 

water  in,  24. 

pectin  compounds  in,  315. 

production  of,  methods  of  increasing,  318, 

319,  342 
protection  of,  330. 
respiration  of,  317. 
ripening  of,  315,  316,  324,  325. 
starch  in,  314. 

struggle  for  existence  of,  312. 
stom."\ta  of,  317. 

s  icculent,  require  more  water,  320. 
sugar  in,  314.  411. 

method  of  increasing,  315. 

thinning  of,  312. 
transpiration  of,  317. 
water  needed  by,  316,  317. 
work  of,  312-325. 
Yeasts  on,  390. 
Fruit  trees,  buds  on  roots  of,  249. 

—  protection  against  drying,  213. 
Fuel  value  of  foods,  173,  196. 
Fumigation  of  plants,  215. 

Function   determines    structure,   179,   185, 

186.*  • 

Fungi.  361-408. 

destroyed  by  lime,  152. 

rotation  of  crops,  160. 

on  roots  of  trees,  150. 

protection  against  by  bark,  256. 

callus,  263. 

Furrow-sliee,  126,*  127. 

Gaillardia.  cross-pollination  of,  303.* 

flower  structure  of,  303.* 
Galloway,  on  freezing,  354. 

—  soil,  129. 

—  plant  diseases,  407. 
Galls.  359. 

Gai-dner,  acknowledgment  to,  x. 
Gardner  on  plant  breeding,  441. 
Gases,  fumigation  with,  215. 


Gases.    See.    also.    Air,    Carbon    dioxide. 

Nitrogen,  Oxygen. 
Gasolene,  lest  for  fats  and  oils,  165. 
Gastric  juice,  171. 
Gaye,  on  soil,  109. 
Gelatin  for  bacterial  cultures,  368,  369, 

—  mould  cultures,  395 
Generation,  spontaneous,  365. 
Geotropism,  88.*  89,*  90,  91,*  92,  93,*  94,  95, 

98,*  99,  264,  308. 
Geranium.    See  Herb  Robert. 
Geranium,  air  passages  in,  280. 
behaviour  of  seeds  of,  71. 
flower  of.  position  of.  307. 
stem  of,  224. 
Geranium,  Ivy,   effect   of  cold   on  chloro- 
phyll, 354. 

—  leaf  mosaic  of,  219. 
Germ,  1,*  2,*  3,*  4,*  20*,  56,  58.* 

contact  of,  with  cover,  20. 

osmotic  action  of,  17. 

See,  also.  Seed. 
Germicide,  364. 
Germination.     See  Seed. 
Giant  Prune.     See  Prune,  Giant. 
Gibson,  on  pollination,  307. 
Girder,  266. 
Girdling  increases    fruit  production,   257, 

318. 
Gladiolus,  leaf  structure  of,  201. 

protection  of,  against  drying,  217. 
Glauber's  salt  in  soil,  158. 
Gleditschia.     See  lioney  Locust. 
Glucose.     See  Sugar. 
Gluten,  177,  178.  437. 
Glycerine  for  shrinking  cells,  390. 

a  product  of  saponification,  170,  171. 
Gnaphaliiim.    See  Immortelle. 
Goodyera.    See  Plantain,  Rattlesnake. 
Gophers  bury  seeds,  69. 
Gorse,  331,  343.* 

effect  of  saturated  atmosphere  on,   341, 
343.* 
Grafting.  248.  249,  433. 
Grains,  chaff  of,  holds  water,  29. 

conveyance    of    food    to    seeds    of,    313, 
314. 

growth  at  nodes  of,  250. 

proteid  in.  177. 


468 


INDEX 


Grains,  starch  in,  177. 

ovary  of,  289. 

pollen  of,  289. 

carried  by  wind,  300. 

stigma  of,  289. 

style  of.  289. 

time  for  cutting,  314. 
Grape  attracts  insects.  299. 

fruit  production  of,  increased  by  bending, 
318. 

girdling,  257. 

—  of,  stomata  of,  317. 
pith  of,  269. 

protection  of  pollen  by,  295. 

root  of,  162. 

self- sterility  of,  309. 
stem  of,  268. 

rigidity  of,  269. 

tendrils  of,  272. 
Grasses,  are  shallow-rooted,  134. 
chaff  of,  holds  water,  29. 
germination  of,  72. 
growth  at  nodes,  250. 
leaf  scar  of,  212. 
ovary  of,  289. 
pollen  of,  289. 

carried  by  wind.  300. 

position  of  leaves  of,  217. 

protection  of,  against  drying,  213,  334. 

—  —  —  animals,  222. 
relation  to  light,  265. 
rhizome  of,  277. 
stigma  of,  289,  292. 
stomata  of,  196. 

•  style  of,  389. 

Gravity,  effect  of.  on  direction  of  growth  of 
root  and  stem.  88,*  89,*  90,  91,*  92, 
93,*  94,  95,  98.*  99,  264.  276,  277. 
effect  of,  on  direction  of  growth  of  dower 
and  fruit,  308. 

Gravel  stops  rise  of  water  in  soil,  115. 

Gray,  on  aestivation,  213. 

Green  flowers,  cause  of,  349,  359. 

—  manures,  150,  384. 

—  rays,  partially  cut  out  by  potassium 

bichromate,  265. 

—  rays    partially    cut     out    by    cupra- 

ammonia,  265. 
Ground,    See  Soil- 


Ground-squirrels  bury  seeus,  69 
Growth  at  nodes,  249,  250. 

correlations  of,  79,*  359,  360. 

effect  of  heat  on,  252, 

light  on,  253. 

water  on,  116,*  117,  252. 

food  required  for,  253. 

force  of ,  in  stem,  73,*  74,*  75,*  76.* 

root,  81,  82,*  83,  84,*  85. 

of  leaves,  inequalities  of,  251. 

oxygen  necessary  for,  5.  6,*  32,  33,*  34,** 
35,  36,  37,*  38,  39,*  40,  125.  126.  281.* 
283,  326. 

region  of  differentiation,  229. 

in  root,  85,*  86. 

stem,  77,*  78.* 

relation  of,  to  osmosis,  64-68. 

temporary  vs.  permanent,  67. 

the  three  regions  of,  249.* 
Guano  as^a  fertilizer,  148,  153. 
Guard-cell,  197,  198,*  199,*  200.  208,*  209," 
210,*  211.* 

artificial,  210,*  211.* 
Gums  lessen  transpiration,  214,  216.  333. 
Gymnocladus.    See  Kentucky  Coffee  Tree. 
Gypsum.    See  Lime  sulphate. 

Habit  of  plant,  264. 

Haemoglobin,  176. 

Hairs,  absence  of,  from  water  plants,  339. 

effect  of  light  on.  347. 

—  protect  against  animUls,  221,  256, 

drying,  213,  214,  333,  334,*  3o5.* 

• water  and  dust,  215. 

Hamamelis.    See  Hazel,  Witch. 
Hamburg,  cholera  epidemic  of,  372,  373.* 
Hanging  drop,  293,*  395,  405. 
Hardiness,  355,  412,  413. 
Hardpan,  106,  351. 

alkali,  159. 
Harper,  acknowledgement  to,  x. 
Hartley,  on  plant-breeding,  434,  441. 
Harwood,  on  plant-breeding.  434. 
Hawkweeds,  behavior  of  scale  leaves,  347. 
Hawthorn,  food  in  buds  of,  253. 

protection  of,  222. 
Hay,  sweating  of,  388. 

time  for  cutting,  314. 
Hays,  on  plant-breeding,  433,  441. 


INDEX 


469 


Hazel,  pollen  of,  carried  by  wind,  300. 

starch  in,  during  winter,  259. 
Hazel,  Witch,  dispersal  of  seeds,  321. 
Heart  wood,  244,  245. 
Heat,  as  preservative,  386. 

effect  of,  on  absorption  by  root,  332. 

bacteria,  363,  364. 

—  —  —  direction  of  growth  of  stem  and 

root,  88,  89. 

—  —  —  evaporation,  115. 
flora,  351,  356. 

flower  and  fruit  production,  347. 

—  —  —  growth,  252. 

leaf,  345. 

Mould.  394. 

opening  and  closing  of  flowers, 

296. 
effect  of  on  plants,  352,  353,  354.*  355-358. 
transformation  of  fat  into 

starch,  259. 

transpiration,  207. 

entrance  of,  into  seed,  42,  *  43. 

excessive,  injurious,  352. 

of  respiration,  35,  36*,  287. 

lack  of,  kills  plants,  352-354. 

prevents  chlorophyll  formation. 

354.* 

—  —  preserves  foods,  etc.,  386. 

—  —  produces  rosette  form,  357. 
needed  by  plant,  326. 

—  to  awaken  seed,  4,  5,*  6. 
set  free  by  flowers,  287. 
seeds,  35,  .  6.* 

Heath  plants  love  sour  humus,  351. 

protection  of,  against  drying,  213,  333. 
Helianthus.    See  Sunflower. 
Heliotropism,  264.  346. 
Hemizonia.     See  Tarweed. 
Hen  •  and  •  chickens,  protection  of,  against 
drying.  215. 

storage  of  water  by,  334. 

transpiration  of,  216. 

water  reservoirs  of,  215. 
Herb  Robert,  protection  of  pollen  of,  295. 
Hereditary  percentage,  436,  442. 
Heredity,  411,*  413,*  416,*  422,  423,*  424,* 
425*,  426,*  427,*  428,  429,*  434,  436.  442. 
Hickory,  flower-buds  of,  286. 

path  of  water  in.  226. 


Hickory,  preparation  for  flowering  of,  286 

seed-cover  of,  holds  water,  29. 

wood  of,  230. 
Hieracium.    See  Hawkweed. 
Hilgard,  acknowledgment  to,  x. 

—  on  soils,  126,*  160. 
Hilum.  1,*  2. 

as  place  for  entrance  of  water,  10. 
Hippuris,  342. 
Histology  of  flower,  290,*  291.* 

—  fungi,  395,*  396,*  397,*  399,*  402,*  403,* 

404,*  407.* 

—  leaf.    196-198.*   199*-201,*   202,*  208,* 

209,*  333,  334,*  335,*  336.*  337,*  338,* 
340,*  344,*  345,*  402,*  403,*  404.* 

—  leaf-stalk,  212. 

—  root,  120,*  121. 

—  seed,  65,*  66,  67,  177,  178. 

—  stem,  224*-227,*  228-230.*  231,  232,*  233, 

234*-236,*  267,*  268,*  328.   333,*  334,* 
335.* 
Holly,  cuticle  of.  334.* 

protection  of.  against  animals,  222. 

drying,  333,  334.* 

transpiration  of.  204. 
Hollyhock,  rust  of,  40fr. 
Holmes,  on  fertilizers,  153. 
Honey.    See  Nectar. 

Honey  Locust,  protection  of.  against  ani- 
mals. 222. 
Honeysuckle  family,  cross  -  pollination  of. 
303. 

flower,  position  of,  307. 
Hop,  cross-pollination  of,  302. 

dispersal  of  seeds  of,  322-323.* 

twining  of,  275. 
Hopkins,  work  of,  434-439. 
Horehound,  hairy  covering  of  leaf,  213. 
Hornblende,  107. 
Hornwort,  339. 
Horse-beau,  germination  of,  81,  82,*  86. 

micropyle  of,  10. 

seed  of,  stnieture  of,  1,*  2. 

seed-leaf  of,  contrasted  with  foliage  leaf 
180-186. 

function  of,  178,  179. 

microscopic  structure  of,  65,*  66. 

Horse-chestnut,  flower-buds  of,  286. 

hairy  covering  of  leaf  of,  213. 


470 


INDEX 


Horse-chestnut,  preparation  of,  for  flower- 
ing, 286. 

See,  also,  Bnckeye. 
Horse-t.'iil,  protection  of,  against  animals, 
223. 

rhizome  of,  277. 
House  plants,  care  of,  132,  136. 
Houstonia,  cross-pollination  of,  305. 
Howard,  on  mosquitoes,  380. 

on  plant  diseases,  407. 
Hubrecht,  on  mutation,  453. 
Hugging  the  ground  as  protection  against 

animals,  223. 
Humulus.    See  Hop. 
Humus,  104. 

as  fertilizer,  148. 

colors  soils,  107. 

fixes  plant-food,  145. 

of  forest,  107. 

plant-food  found  in,  107,  351. 

properties  of,  107. 

retains  water  in  soil,  132.  133. 

test  for,  155. 
Hunn,  on  gardening,  249,  263. 
Hunt,  acknowledgment  to,  x. 
Hyacinth,  preparation  of,  for  flowering,  286. 

stomata  of,  196. 

storage  of  food  in.  286,  313. 

water,  340. 
Hybrids,  character  of,  411,*  413,*  416,*  422, 
423,*  424,*  425,*  426,*  427,*  428,  429,* 
434. 

defined,  421. 
Hydrochloric  acid.  See  Acid,  Hydrochloric. 
Hydrogen,  a  product  of  decomposition  of 
cellulose,  381. 

in  foods,  175, 

peroxide  as  disinfectant,  364. 
Hydrolysis,  167. 

of  starch,  167-169. 
Hydrotropism,  95,*  96,*  97,  98. 

Ice,  method  of  using,  5.* 

role  in  soil-formation,  109. 
Ice  Plant,  protection  of,   against  drying, 
215. 

water  reservoirs  of,  216/- 
Hes,  on  plant-breeding,  441. 
Ilex.    SeeHoUv. 


Illinois   Experiment  Station,  plant-breed- 
ing at,  434-439. 

river,  sewage  of,  382. 
Immature  seeds,  germination  of,  43. 
Immortality  of  bacteria,  368. 
Immortelle,  protection  of,  against  drying, 

334. 
Immunity,  379. 
Impatiens.    See  Jewelweed. 
Improved    Beach    Plum.     See    Plum,   Im- 
proved Beach. 
Inch  Plant.     See  Wandering  Jew. 
India  Ink,  injection  of  wood  with,  237. 
Indigo  rays  cut  out  by  potassium  bichro- 
mate, 265. 
Infectious  diseases,  380. 
Injury,  effect  on  the  plant  of,  79.*  86,  263. 
Insects  bury  seeds,  69. 

destroyed  by  crop  rotation,  160. 

lime,  152. 

how  supplied  with  oxygen,  176. 

method  of  alighting  at  flower  of,  307. 

open  flowers,  308. 

partial  to  certain  colors,  298. 

protection  against,  by  bark,  256. 

—  of  flowers  from,  308,  309. 

fruits  from,  320. 

role  of,  in  pollination,  289,  291.  297-311. 

trapped  by  plants,  172. 

unwelcome.  308. 

visual  powers  of,  300. 
Insectivorous  plants,  172. 
Iodine  solution,  preparation  of,  164. 

test  for  starch,  164,  367. 
.Iodoform  as  disinfectant,  364. 
Ipomcea.    See  Moonflower,  Morning  Glory 

and  Sweet  Potato. 
Iris,  cross-pollination  of.  304.* 

flower  of,  platform  of,  307. 

sti-ucture  of,  304.* 

leaf  of,  structure  of,  199,*  201. 

protection  of,  against  drying,  217,  333,  334. 

water,  214,  294. 

pollen,  294. 

rhizome  of,  277. 

stomata  of,  196,  199,*  208,*  209.* 

storage  of  food  in,  260.  313. 
Iron,  needed  by  plants,  139, 
Iron  chloride,  171. 


INDEX 


471 


Irrigation.  130,  131,  135. 
effect  of,  on  fruit.  343. 
Ivy,  Boston.     See  Ivy,  Japanese. 
Ivy.  English,  aerial  roots  of.  275.* 

—  attracts  insects,  299. 

—  leaf-mosaic  of.  219. 

—  starch  in  leaf  of.  182.* 

Ivy.  Japanese,  leaf -mosaic  of,  219. 

—  tendrils  of,  274. 

Ivy  Geranium.     See  Geranium,  Ivy. 

Jam,  process  of  making,  315. 
Japanese  Ivy.     See  Ivy,  Japanese. 

—  Plum.     See  Plum,  Japanese. 
Jasmine,  climbing  of,  270. 

Jasmine,  Yellow,  protection  of  root  of,  161, 

162. 
Javelle  water,  23. 
Jelly,  process  of  making,  315. 
Jewelweed,  protection  of  pollen  by,  294. 
Jimson  Weed.    See  Thorn  Apple. 
Johnson,  on  bread,  178. 
Johnson,  on  soil,  109,  133. 
Juglans.    See  Walnut. 
J  uncus.     See  Rushes. 
Juniper,  seed  dispersal  of.  325. 
wood  of,  230. 

Kentucky  Coffee  Tree,  leaf  scar,  212. 
Kerner  and  Oliver,  on  pollination,  307. 

—  —  —  protection  of  pollen,  294. 
King,  on  irrigation  and  soil,  109,  129,  133, 

153. 
Knot-grass.     See  Polygonum. 

Laburnum,  flower  of,  position  of,  307. 
Lactic  acid.    See  Acid,  Lactic. 
Lactuca.     See  Lettuce. 
Land.   See  Soil. 

Land  plants.     See  Plants,  Land. 
Land  plaster.    See  Lime  sulphate. 
Landslides,  experimental  formation  of,  111. 
Lappa.    See  Burdock. 
Larkspur  n^eds  light  for  germination,  47. 
Lateness,  412. 
Lathyrus.    See  Pea,  Sweet. 
Laurel,  air-passages  of,  280. 
Leaf  absorbs  light,  201. 
air  in,  187*-190. 


Leaf,  air-spaces  in.  198,*  199,*  338.* 
as  absorbing  organ,  200. 
as  mulch,  115. 
arrangement  of,  220,*  221.* 
benefited  by  washing,  215. 
absorbs  carbon  dioxide,  200. 
—  oxygen,  194,  195. 
autumn,  332. 

bleaching  of,  with  lye  and  alcohol,  225. 
coloj;  of,  in  autumn,  332. 
compared  to  root,  200,  201. 
decomposes  carbon    dioxide,   191,*   192,* 

193,*  194,  195. 
development  of,  250,*  251. 
effect  of  cold  on,  354.* 

dryness  on,  345. 

freezing  on,  353. 

heat  on,  345. 

light  on,  184,   185,  344.*  345,*  346, 

347. 

water  on,  341,  342,*  343.* 

wind  on,  345. 

energy  absorbed  by,  196,  201. 
evaporation  from.     See  Leaf,  transpira- 
tion of. 
fall  of,  212,  332. 

caused  by  spraying,  215. 

foliage,  contrasted  with    seed-leaf,   180- 

186. 
follows  sun,  217,  218,  345. 
food  in,  181. 
function  of.  181-223. 
gives  off  carbon  dioxide,  191.*  192,*  193,* 

194,  195. 
hinge-like  joints  of,  218,  220. 
injured  by  fumigation  and  sprays,  215. 
internal  structure  of,  196-212  (198,*  199,* 

201,*  202,*  208,*  209,*  210.*  211.* 
microscopic  structure  of,  196-198,*  199*- 

201,*  202,*  208,*  209,*  333,*  334,*  335,* 

336,*  337,*  338,*  340,*  344,*  345,*  402,* 

403,*  404.* 
method  of  fixing  air-tight    in  stopper, 

205.* 
movements  of ,  217,  218.*  219,*  220.*  221.* 
of  water  plants,  337,*  338.* 
osmosis  in,  242. 
position  of,  216,  217,  218.* 
propagation  by,  433. 


472 


INDEX 


Leaf,  protection  of.  against  animals  by  bit- 
ter taste.  222,  223. 

hairs,  221. 

—  —  hugging  the  ground,  223. 

poisonous  substances,  222. 

prickles,  221. 

spines,  221,  334. 

teeth,  222,  334. 

texture.  223. 

thorns,  221. 

enwrapping,  251,  261. 

drying,  by  hairs,  213,  333,  334,* 

335.* 

position,  217,  218.* 

reduction  of  surface,  215, 

332,  342.* 

in  number  of  stomata, 

215,  235,  336.* 

— rolling,  folding,  etc.,  213, 

334. 

sunken  stomata,  215,  335, 

337.* 

thicker  cuticle,  333,    334,* 

337,*  338.* 
—  —  —  —  —  water -proof     substances, 

214,  251,  333,  334.* 
water  -  retaining  substan- 
ces, 216. 
raises  sap,  242. 
respiration  of,  194,  195. 
scale,  347. 
shade,  3^4,*  345.* 
sleep  position  of,  218.* 
starch  formation  in,  182-203  (182,*  184,* 
186,*  191,*  192.*  193,*  198.*  199,*  201,* 
202*). 
starch  in.  181.  182.*  183. 
storage  of  food  in,  260. 
strength  of,  how  secured,  267.* 
sun.  344.*  345.* 
transpiration    of.    203*- 206.*    207,    208,* 

209,*  210,*  211*-218,*  317,  328,  348. 
turns  toward  light.  217-219. 
unequal  growth  of  opposite  sides  of,  251. 
variegated,  starch  in.  185. 
veins  of.  198,*  199,*  225,  267.* 
water,  337,*  338.*  339.*  340.* 
withdrawal  of  nutriment  from,  in  au- 
tumn. 332. 


Leaf,  work  of,  163-285. 

See,  also,  Seed-leaf  and  Stomata. 
Leaf  green.    See  Chlorophyll. 
Leaf-mold,  107. 

—  capacity  for  holding  water  of,  132. 

—  test  for  humus  in,  155. 
Leaf-mosaic,  219. 
Leaf-scar,  212,  245,  332. 

Leathery  texture  protects  against  animals, 

223. 
Lenticel,  232,*  278,  279.* 
Leontodon.    See  Dandelion. 
Lettuce,  Prickly,  sun-  and  shade-leaves  of, 

344.* 
Levees,  protected  by  plants,  277. 
Life,  length  of,  in  plants,  286. 
Light,  absorbed  by  leaves.  201. 

affects  absorption  of  carbon  dioxide.  207. 

chemical  action  caused  by,  182  *  184,*  185 
195,  196,  201,  316,  364,  382. 

kills  bacteria,  364,  382. 

effect  of,  on  chlorophyll,  184,*  185. 

color  of  fruit,  316. 

—  —  —  direction  of    growth    of   plant, 

264,  346. 

—  —  —  evaporation  from  the  soil,  115. 
eye,  196. 

flowers,   295,   296,  298,   308,   347, 

348. 
form  of  plant,  184,*  185,  261,  327, 

328,*  329,*  344,*  345*-348. 

fruit.  308.  342.  347. 

— fruit  and  flower  production,  347. 

—  —  —  germination,  47. 
growth.  253. 

leaves,   184,*   185,  217-219,   344,* 

345,*  346. 

Mould,  394. 

portion  of  effective  in  heliotropism,  265. 

starch  formation,  196. 

relation  of,  to  self -pruning  of  trees,  etc. 

261. 
starch  formation,  182,*  184,*  185, 

201. 

stem,  264,346.    ' 

stomata,  207-209. 

transpiration,  207. 

electric,  for  growing  plants  .346. 
needed  by  plants,  326. 


INDJUX 


473 


Light  filter,  265. 

Lilac,  food  in  buds  of,  253. 

Mildew  of,  406,  407.* 

starch  in.  during  winter,  259. 

transpiration  of,  204. 
Lilium.    See  Lily. 
Lily,  embryo-sac  of,  291,* 

leaf-scar  of,  212. 

stomata  of,  210. 

storage  of  food  in,  313. 
Lily,  Pond.    See  Lily,  Water. 
Lily.  Water,  282,  337.  339. 
Lima  Bean.    See  Bean,  Lima. 
Lime  as  fertilizer,  151,  153, 154. 

benefits  puddled  soil,  129. 

destroys  insects  and  fungi,  152- 

effect  of,  on  flora,  350. 

flocculates  clay,  152. 

for  softening  water,  152. 

how  supplied  to  soil,  151. 

needed  by  plants,  139. 

promotes  decomposition,  152. 

sets  free  plant-food.  152. 

sweetens  sour  soil,  152. 

test  for,  157. 
Lime    carbonate,    dissolved     by    cavbouic 
acid,  140. 

chloride  as  disinfectant,  364. 

oxalate,  crystals,  232.*  254. 

sulphate,  as  fertilizer,  151. 

—  etched  by  roots,  144. 

—  for  casts,  76. 

germination  experiments,  44. 

water,  34,  139. 
Linden,  change  of  fat  to  starch  in,  259. 

dispersal  of  seeds  of,  322.* 

fat  of,  in  winter,  259. 

protection  of  pollen  of,  294. 
LinnaBus,  floral  clock  of.  295. 
Linum.     S^e  Flax. 
Lipase,  170. 

Liriodendron.     See  Tulip  Tree. 
Listerine  as  disinfectant,  364. 
Live-f or-ever,  protection  of,  against  drying, 
215. 

storage  of  food  in,  260. 

—  —  water  in,  334. 
water  reservoirs  of,  216. 

Loam,  108. 


Lockjaw,  328.  380. 

Loco  weeds,  222. 

Locust,  protection  against  animals,  222. 

Lodeman,  on  pruning,  264. 

—  spraying,  407. 
Lonicera.    See  Honeysuckle. 
Loughridge,  acknowledgment  to,  x. 

on  soil  testing,  155,  160. 
Lubbock,  on  pollination,  307. 
Lupine,  dispei'sal  of  seeds  of,  320. 

leaves  of,  follow  sun,  218. 

root-tubercles  of,  149, 

seed-covers  of,  hinder  absorption,  25. 
Lupine,  Yellow,  visited  by  bees,  299. 
Lupinus.     See  Lupine. 
Lye  absorbs  carbon  dioxide,  34. 

and  alcohol  for  bleaching  leaf,  225. 

softens  bark,  248. 
Lyle,  on  plant-breeding,  453. 

MacDougal,  on  mutation.  453. 
Madia.    See  Tar-weed. 
Magnesium  needed  by  plants,  139. 
Magnolia,  air-passages  of,  280. 
Mahonia,  transpiration  of,  204. 
Maize.    See  Corn. 
Malaria,  380. 
Mallow,  leaf  of,  follows  sun,  218. 

Rust  of,  406. 
Mallow  family,  cross-pollination  of,  303. 
Manure  as  general  fertilizer,  148,  153. 

as  mulch,  115. 

benefits  puddled  soils,  129. 

decomposition  of,  383. 

green,  150,  384. 

nitrogen  in,  147. 
Maple,  bird's-eye,  262. 

dispersal  of  seeds  of,  321,  322.  323.* 

flower-buds  of.  286. 

food  in  buds  of,  253. 

preparation  of,  for  flowering,  286. 

protection  of,  against  drying,  213. 
Maple,  Sugar,  run  of  sap  of,  in  spring,  243. 

259. 
Marble  as  fertilizer.  151. 

dissolved  by  carbonic  acid,  141. 

etched  by  roots,  144. 
Marking,  apparatus  for,  78.* 
Marl  as  fertilizer,  151. 


474 


INDEX 


Marnibium.     See  Horehound. 

Marsh  gas,  381, 

Massee,  on  plant  diseases,  407. 

Material,  economy  of,  in  construction,  265. 

266. 
McKenny,  on  fertilizers,  153. 
Meadows  killed  by  flooding,  125. 

remain  in  good  tilth,  129. 
Meanders,  experimental  formation  of.  111, 
Means,  on  fertilizers,  153. 
Meat,  preservation  of,  385,  386. 
Medicago.    See  Alfalfa,  Bur  Clover. 
Medullary  rays,  232,*  233,  258. 
Melampyrum.    See  Cow  Wheat. 
Mclilotus,  leaves  of,  follow  sun,  218. 
Mentha.    See  Mint. 
Mercurialis.    See  Dog's  Mercury. 
Mesembryanthemum.    See  Ice  Plant. 
Metabolism.  See  Chemical  action  Iti  plants. 
Mexican    Morning-Glory.        See  Morning- 

Glory.  Mexican. 
Microscopic  structure.   See  Histology. 
Mildew,  406,  407.* 
Milk,  action  of  f elements  on,  172. 

as  emulsion,  170. 

bacteria  of,  372-378. 

souring  of,  376. 
Mica,  107. 
Micropyle,  8,*  9. 

admits  air,  30,*  31,  32. 

function  of,  10-24. 

should  be  in  contact  with  soil,  21,*  22.* 
Mignonette  attracts  insects,  299. 
Milling.  178. 
Milner,  on  foods,  173. 
Mimulus.    See  Monkey  Flower. 
Mineral  substances  in  soil,  136-160. 
Mint,  rhizome  of,  277. 

family,  cross-pollination  in,  303. 
Missing  links,  443,  452. 
Mississippi,  382. 

Mitchella.   See  Partridge-berry. 
Moisture.   See  Water. 
Molasses,  369,  389. 
Molybdate  of  Ammonium.  See  Ammonium 

molybdate. 
Monkey  Flower,  stigma  of,  292. 
Monkshood,  protection  of  pollen  of,  294. 

root,  161. 


Monocolytedons  are  mostly  shallow-rooted. 
135. 

behavior  of  leaves  of,  in  dark,  347. 

characterized,  226. 

have  no  cambium,  228. 
^lonoecioiis  plants,  302. 
Monstrosity,  420,  421,  449.* 
Moon   Flower,  seed -cover  of,  hinders  ab- 
sorption, 25. 
Moor  plants,  protection  against  drying,  333. 
Moors,  absorption  difficult  in,  336. 
Moore,  on  bacteria,  384. 
Morphologj',    experimental.      See     Plant, 

form  of. 
Morning-Glory,  germination  of,  81. 

seed-cover  of,  hinders  absorption,  25. 

self-  vs.  cross-pollination  of,  301,  302. 

twining  of,  275. 

Mexican,  seed-cover  of,  hinders  absorp- 
tion, 25. 
Moss  Rose.     See  Rose,  Moss. 
Moths  visit  night-blooming  flowers,  300. 

visual  powers  of,  300. 
Mould,  precautions  against,  28,  72,  100,  102, 
397. 

bread,  391,*  392,*  393,*  394,*  395,*  396.* 

green,  396,  397.* 
Movements  of  flowers,  296,  297. 

—  leaves,  217,  218,*  219.*  220,*  221.* 
Mucor  stolonifer,  391. 
Mulch  for  soil,  40,  115,*  116,*  117,  125,  129. 

133,  135,  353. 
Mullein,  hairy  covering  of  leaf  of,  213. 

protection  of,  against  animals,  221. 

dryness,  334,  335.* 

Miiller,  on  pollination,  307. 
Mushroom,  power  of  growth  of,  77. 
Mustard,  effect  of  light  on  flowers  of,  298. 

germinati  jn  of,  8. 
Mustard  family,  cross-pollination  in,  303. 
Mustard,  Yellow,  structure  of  leaf  of,  196. 

197,  198,*  200-202. 
Muscle-forming  foods,  176. 
Mutation,  330,  442-444,*  445,*  446,*  447*-453. 
Mycelium,  392,  402. 

Nails  used  to  promote  fruit  production,  319. 
Narcissus,  pollen  of,  293. 

starch  formation  in,  183,  191.*  193.* 


INDEX 


475 


Narcissus,  stomata  of,  196. 
Nasturtium,  leaf-stalk  of,  acts  as  tendril, 
270. 

pollen  of,  293. 
Natural  selection,  330,  331,  442-453. 
Nectar  attracts  insects,  300. 

protection  of,  295. 
Nectarine,  origin  of,  420. 
Needs  of  plant,  326. 
Nepenthes,  172. 
Nerium.     See  Oleander. 
Nettle,  pollen  of,  carried  by  wind,  300. 

protection  of,  against  animals,  221. 
Newman,  on  bacteria,  408. 
Nicotiana.    See  Tobacco. 
Nightshade  family,  cross-pollination  of,  303. 
Nitragin,  385. 

Nitrates,  produced  by  bacteria,  383-385. 
Nitrate    of   potassium.     See  Potassium 

nitrate. 
Nitrate  of  silver.     See  Silver  nitrate. 
Nitrate  of  soda.    See  Sodium  nitrate. 
Nitric  acid.     See  Acid,  Nitric 
Nitrites  produced  by  bacteria,  383-385. 
Nitrogen  combines   with   starch    to  form 
proteids,  253. 

conserved  by  plants,  176. 

effect  of,  on  plant,  349,  350. 

escapes  from  soil,  148,  149. 

how  supplied  to  soil,  147,  148,  149,*  150. 

in  air,  149,  383-385. 

—  beans,  177. 

—  eggs,  177. 

—  peas,  177. 

—  percolating  water,  149. 
needed  by  animals,  176. 
plants,  139,  140,*  176. 

prepared  for  plant  by  bacteria,  149,*  150, 
383-385. 

prepared  for  plant  by  fungi,  150. 

produced  by  bacteria,  383. 

promotes  leaf-,  rather  than  fruit-produc- 
tion, 318. 

selected  by  plant,  161. 

taken  from  air  by  bacteria,  383-385. 

some  plants,  149. 

test  for,  in  soils,  155. 

waste  of,  by  animals,  176. 
Node,  327. 


Node,  growth  at,  249,  250. 

Notching,  to  increase  fruit  production,  318. 

Nucleus,  65,*  66,  290,  291,*  311. 

Nuphar.    See  Spatterdock. 

Nutrition.    See  Food. 

Nuts,  absorp  ion  of  water  by,  7,  23,*  29. 

protection  of,  against  drying,  317. 

seed  of,  320. 

Nymphaea.    See  Lily,  Water, 

Oak,  cambium  of,  232,*  246. 

fibrous  bundle  of,  226. 

food  conveyed  to  fruit  of,  313. 

latent  buds  of,  262. 

path  of  water  in,  226,  230,  232,*  233,  234,* 
235. 

pollen  of,  carried  by  wind,  300. 

starch  in,  259. 

stem  of,  microscopic  structure  of,  232,* 
233,  234,*  235,  246. 

wood  of,  compared  with  wood  of  Pine, 
235,  238. 
Oat  contains  no  pepsin,  172. 

germination  of,  47. 

stomata  of,  196. 

ovary  of.  290.* 

pollen  of,  290.* 

stigma  of,  290.* 

style  of.  290.* 
Oat,  WiLl,  seeds  of,  bury  themselves,  71. 
Oat  Rust,  4C4,  405. 
Oat-smut,  400-401. 
Odor  attracts  insects,  299,  300. 
CEnothera.     See  Primr^  se.  Evening. 
Oil,  emulsification  of,  169,  170. 

energy  from,  173. 

formation  of,  201, 

in  eggs,  177. 

—  fruits,  314. 

—  growing  region,  253. 

—  seeds,  165,  177,  437. 
injures  leaf,  215. 
produced  from  starch,  314. 
saponification  of,  170,  171. 
test  for,  105,  259. 

See,  also.  Fat. 
Oil,  C  coanut,  169,  170. 
Oil,  Corn,  437. 
Oil,  Cottonseed,  147,  169, 170. 


476 


INDEX 


Oil.  Olive,  169, 170,  171. 
Oily  seeds,  transformation  of  food  in.  314, 
Oleander,  protection  of,  against  drj'ing,  215. 
333,  337.* 

transpiration  of,  204. 
Olive  oil.    See  Oil,  Olive. 
Onion,  germination  of,  47,  72,  81. 

pollen  of,  293. 

roots  of,  86. 

storage  of  food  in,  313. 
Opening  and  closing  of  flowers.  See  Flower. 
Opium  Poppy.    See  Poppy,  Opium. 
Opuntia.    See  Prickly  Pear. 
Orange  rays  cut  out  by  cupra-ammonia,  265. 
Orchids,  cross-pollination  of,  306,  307, 
Orchis.    See  Orchids. 
Oriental  Poppy.    See  Poppy,  Oriental. 
Origin  of  species,  441-453. 
Osmosis,  122,  123,*  124. 

generates  pressure,  60,  61,*  62.* 

in  seed,  60,  63,  64,  67. 

makes  stem  rigid,  269. 

of  leaves,  242. 

relation  of,  to  growth,  64-68. 

through  seed-cover,  16,*  17,  18,  19,*  20. 
Osmotic  pres.sure,  measurement  of,  62,*  63. 
Ovary,  288,*  289,  290.* 

correlation  of,  360. 
Ovule,  288,*  312. 
Oxalate  of  ammonium.     See  Ammonium 

oxalate. 
Oxalate  of  lime.     See  Lime  oxalate. 
Oxalic  acid.     See  Acid,  Oxalic. 
Oxalis,  dispersal  of  seeds  of,  321. 

opening  and  closing  of  flowers  of,  295. 

protection  of,  against  water,  214. 

sleep  position  of  leaf  of,  218. 
Oxbows,  experimental  formation  of,  111. 
Oxidation,  as  source  of  energy,  35,  173. 

brought  about  by  ferments,  173. 

See,  also.  Combustion  and  Respiration. 
Oxygen,  absorption  of,  33,  34,*  35,  36,  175, 
194,  195,  200,  287,  317,  388.  390. 

given  off  by  leaf,  191,*  192,*  193,*  194,  195. 

how  supplied  to  organisms,  176. 

needed  for  growth,  5,*  6,  32,  33,*  34,*  35, 
36,  37,*  38,  39,*  40,  125,  126,  281.*  283. 
326. 

See,  also.  Air. 


Papaver.     See  Poppy. 

Palisade  cells,  198,*  199,*  200.  201. 

effect  of  light  on,  345. 

poorly  developed  in  water-plants,  339. 
Palms,  pollen  of,  carried  by  wind,  300. 
Pancreas,  169. 
Pancreatic  juice,  169-172. 
Pansy  hybrids,  428. 
Parasitic  bacteria,  380. 
Parenchyma  of  wounds,  319. 

See,  also.  Cell  parenchyma,  Bast  paren- 
chyma and  Wood  parenchyma. 
Parental  characters.     See  Heredity. 
Paris,  plaster  of.     See  Lime  sulphate. 
Parsley  family,  flowers  of,  298. 
Parsnip,  flowers  of,  attract  bees,  299. 

storage  of  food  in,  313. 

sugar  in,  122. 
Partridge -berry,  cross -pollination  of,  304. 

305.* 
Passiflora.     See  Passion  Flower. 
Passion  Flower,  272. 

calyx  of,  288. 
Pasteur's  solution,  formula  of,  398. 
Pasteurization  of  milk,  377. 
Pastinaca.     See  Parsley. 
Pastures,  remain  in  good  tilth,  129. 
Paving,  keeps  air  from  roots,  126. 
Pea,  89,  141-144. 

absorption  of  water  by  seed  of,  7. 

contains  no  pepsin,  172. 

cross-pollination  of,  306. 

flower  of,  opened  by  bees,  308. 

platform  of,  307. 

food  in,  177. 

germination  of,  47. 

leaves  of,  follow  sun,  218. 

pocket  of  seed  of,  20. 

protection  of  fruit  of,  320. 
Pea,  Sweet,  pollen  of,  292,  293. 
Pea  family,  cross-pollination  in,  303, 

dispersal  of  seeds  in,  321. 

protection  of  pollen  in,  294. 

root-tubercles  of,  149,  384.  385. 

tendrils  of,  272. 
Peabody,  on  foods,  173. 
Peach,  escape  from  seed-cover  of,  5-1. 

protection  of,  against  drying,  214,  317. 

fruit  of.  320. 


INDEX 


477 


Peach,  seed-cover  of,  59. 

hinders  absorption,  25. 

path  of  water  in,  9,  24. 

sports  of  (Nectarine),  420. 
Peanut,  air-reservoir  of,  42. 

buries  its  seeds,  70. 

protection  of  fruit  of,  320. 

structure  of  fruit  of,  3,  4.* 
Pear,  epidermis  of  fruit  of,  317. 

hairy  covering  of  leaf  of,  213. 

self-sterility  of,  309, 

stomata  of,  317. 
Pear.  Prickly,  cross-pollination  of,  306. 

effect  of  moisture  and  darkness  on,  329. 
■pearl  ash,  154. 

Peat  bogs,  absorption  difficult  in,  217. 
Peat  moss,  killed  by  lime,  350. 

loves  sour  humus,  351. 
Pecan,  escape  from  seed-covering  of,  54. 

opening  in  seed-cover  of,  8,*  9. 

path  of  water  in  seed-cover  of,  9,  24. 
Pectin  compounds  in  fruits,  315. 
Pelargonium,  behavior  of  seeds  of,  71. 

See  Geranium. 
Penicillium,  396,  397.* 
Pepsin,  171,  172. 
Peptone,  369. 

Perennials,  flowering  of,  286. 
Periwinkle,  leaf-arrangement  of,  220,*  221.* 
Petals,  color  of,  297-300. 

injury  of,  288. 

transformed  into  leaf -like  bodies,  359. 
Petroselium.     See  Parsley. 
Petunia,  crossed  with  tobacco,  432. 
Phaseolus.     See  Bean  and  Scarlet  Runner. 
Phleum.     See  Timothy. 
Phoenix.    See  Date. 
Phlox,  protection  of  pollen  of,  294. 
Phosphoric  acid.     See  Acid,  Phosphoric. 
Phosphonis,    effect  of,   on    production  of 
flowers  and  fruit,  318,  350. 

how  supplied  to  soil,  150,  151. 

needed  by  plants,  139,  140.* 

obtained  from  bones,  150. 

test  for,  in  soils,  155,  156. 

unites  with  starch  in  proteid  formation, 
254. 
Photosynthesis.     See  Starch -formation 
Phylloxera.  162. 


Physiography,  experiments  in,  103-160. 
Picea.     See  Spruce. 
Pinchot,  on  forestry,  245. 
Pine,  cambium  of.  236,*  246. 

correlation  in,  359. 

cross-pollination  of,  302. 

dispersal  of  seeds  of,  321,  322. 

latent  buds  of,  262. 

pollen  of,  carried  by  wind,  300,  .301. 

—  —  vesicles  of,  301. 

protection  of,  against  drying,  333,  334. 

friiit  of,  320. 

wood  of,  compared  with  Oak  wood,  235, 
238. 

microscopic  structure  of,  235,  236.* 

Pine-apple,  trypsin  m,  172. 

Pink  Bean.     See  Bean,  Pink. 

Pink  family,  cross-pollination  of,  303. 

Pitcher  Plant,  pepsin  in,  172. 

Pith.  120,*  121,  269. 

Pits.  227  *  229.  232,*  233,  234,*  235. 

Plants,  action  of,  in  forming  soil,  109. 

alpine,  357,  358. 

chemical  action  in,  1C6-177,  182-196,  253 
254,  258.  2.59.  314-316. 

climbing,  270,  271,*  272,  273,*  274,  275.* 

decay  of,  381. 

dicotyledonous,  226. 

diseases  of,  397,  398,*  399,*  400,  401,  402,* 
403,*  404-407,*  408. 

damage  done  by,  400,  401,  406. 

prevention  of ,  400,  401,  407,  408,  440. 

engineering  principles  illustrated  in  struc- 
ture of,  266,  267.*  268,*  269,  270. 

form  of,  effect  of  correlation  on,  359. 

fungi  on,  359. 

— light  on,    184,*  185,   261,  327, 

328,*  329,*  344,*  345*-348. 

form  of.  effect  of  water  on,  326,*  327,* 
328,*  329,*  330,  331,*  332,*  .333,*  334,* 
335.*  336.*  337,*  338,*  339,*  340,*  341, 
342,*  343,*  344.* 

effect  of  wind  on,  348,*  349,*  350.* 

food  of.  in  soil,  amount  of,  146. 

dissolved    by   carbonic   acid. 

ir9-145. 

fixed  by  clay  and  humus,  145. 

—  —  —  —  set  fi'ce  by  lime,  152. 

—  needed  by,  164-176. 


478 


INDEX 


Plants,  habit  of.  264. 
has  problems  to  solve,  6,  29,  260. 
how  supplied  with  air.  176,  187*-190,  278, 

279,*  280,*  281.*  282-285. 
injury  of,  79.*  86.*  263. 
land  vs.  water,  3:58,  339,*  340,  342. 
length  of  life  of,  286. 
monocotyledonous,  135,  226,  248,  347. 
moncecious,  302. 
needs  of,  6,  326. 
poisonous,  222. 
selective  action  of,  161. 
strength  of,  how  secured,  266,  267,*  268,* 

269,  270. 
struggle  of,  for  existence.     See  Struggle 

for  existence, 
supply  carbon  dioxide  to  aquaria,  285. 
tendril  bearing,  270-274. 
twining,  275,  276. 
water,  characteristics  of,  337,*  338,*  339,* 

340*-342. 
weaving,  270. 
Plant-breeding,  331.  335,  409-411,*  412-413,* 
414,*415,*416,*417,418,*419,*420-423,* 
424,*  425,*  426,*  427,*  428,   429,*  430, 
431*-444,*  445,*  446,*  447,*  448*,  449*- 
453. 
Plant  lice  cause  green  flowers,  349. 
Phmtago.     See  Plantain. 
Plantain,  cross-pollination  of,  303. 
protection  of  pollen  of,  295. 
Rattlesnake,  prefers  coniferous  humus, 

351. 
Water,  342. 
Planting  stick,  40.* 
Plaster  of  Paris.     See  Lime  sulphate. 
Platinum  wire,  366. 
Plow  sole,  126.* 
Plowing,  126,*  127,*  128,*  132. 
Plum,  escape  of,  from  seed,  54. 
flower  of,  431.* 
improvement  of,  by  breeding,   409-411,* 

412,  413,*  414,*  415,*  416,*  417. 
pollination  of,  430,  431.* 
self  sterility  of ,  309. 
See,  also.  Prune. 
Plum,  American,  409,  410,  411,*  412,  413.* 
Apple.  410. 
Bartlett,  410. 


Plum,  Beach,  410. 
European,  409,  411. 
Improved  Beach,  412,  413,*  414.* 
Japanese,  409,  410,  411. 
Pond,  411. 

Stoneless,  415,  416,*  417. 
Plumcot,  415.* 
Plumule,  1,*  2,*  3,*  4.* 

protection  of,  71,*  72,*  79.* 
Pneumonia,  380. 
Pocket  around  caulicle,  20,*  58.* 
Pod,  3. 

Poisonous  plants,  222. 
Pole  Bean.     See  Bean  Pole. 
Pollen,  carried  by  insects,  289,  291,  297-3r . 

wind,  300,  301,  310.  311. 

effect  of,  309,  311. 
exclusion  of,  289. 

germination  of,  290,*  292.  293,*  294. 
injured  by  rain,  294. 
protection  of,  294,  295. 
use  of,  289. 
vitality  of,  294. 
Pollen-tube,  290,*  291.* 
attracted  by  stigma,  293,  294. 
grows  away  from  air,  293. 
Pollination,  289-311,  430-431,*  435,  436. 
cross-,  301. 

effect  on  ovary,  etc.,  309. 
self-,  301. 
Polygonatum.     See  Solomon's  Seal. 
Polygonum,  protection  of,  against  animals, 
223. 
Water-,  335,*  336.*  340.* 
Pond  Lily.     See  Lily,  Water. 
Pond  Plum.     See  Plum,  Pond. 
Pondweed,  339. 

Poor -man's- weather-glass,    behavior    of 
flowers  of,  295,  296. 
protection  of  pollen  of,  295. 
Pop  corn,  7. 

Poplar,  buds  formed  on  roots  of,  249. 
cross-pollination  of,  302. 
flower-buds  of,  286. 
leaf  of,  hairy  covering  of,  213. 
pollen  of,  carried  by  wind,  300, 
preparation  of,  for  flowering,  286. 
protection  of,  against  drying,  214. 
—  —  —  water,  214. 


INDEX 


479 


Poplar,  transpiration  of,  204. 
Poplar,  White,  haii-y  covering,  213. 
Poppy,  needs  light  for  germination,  47. 

position  of  dowers  of,  307. 

protection  of,  against  animals,  222. 
Poppy,  Opium,  427,*  428. 
Poppy,  Oriental,  427,*  428. 
Poppy  hybrids,  427-420.* 
Portulaca.     See  Purslane. 
Potamogeton.     See  Pondweed. 
Potash,  as  plant-food,  139,  140.* 

how  supplied  to  soil,  152. 

increases  fruit  production,  318. 

needed  by  plants,  139,  140.* 

set  free  by  lime,  152. 
Potassii^m,  bichromate,  as  light  filter,  265. 

chloi-ate,  235. 

nitrate,  139, 148,  153. 

permanganate,  364. 
Potato,  correlation  in,  360. 

cuticle  of,  328. 

effect  of  freezing  on,  353. 

light  on,  327,  328.* 

water  on,  326,  327,*  328,*  329,  330. 

eyes  of,  200. 

for  bacterial  cultures,  365,*  366,  367,*  380. 

protection  of  pollen  by,  295. 

starch  in,  328. 

stem  nature  of  tuber  of,  260. 

storage  of  food  by,  260,  297,  313. 

transpiration  of,  328. 
Potato,  Sweet,  twining  of,  275. 
Potato  Vine,  tendrils  of,  270. 
Potentilla.     See  Cinquefoil. 
Powell,  on  praning,  264. 
Preservation  of  foods,  376,  377,  385-388,  397. 
Prickles,  effect  of  light  on,  347. 

protect  against  animals,  221, 
Prickly  Lettuce.    See  Lettuce,  Prickly. 
Prickly  Pear.    See  Pear,  Prickly, 
Primrose,  cross-pollination  of,  305. 

protection  of  pollen  by,  294. 
Primrose,  Evening,  Broad,  446,*  447.* 

—  Dwarf.  445.* 

—  Lamarck's,   mutations   of,    443,   444,* 

445,*  416,  447.* 

—  Pale,  447.* 
Primula.    See  Primrose. 
Propagation.    See  Reproduction. 


Protection  against  animals,  etc.,  by  bark, 
256. 
bitter  taste,  222,  260,  320. 

—  —  —  —  concealment,  200,  320. 
— hairs,  221,  256,  200. 

—  —  —  —  hug  ing  the  ground,  223. 

—  — hard  cos^erings,  320. 

—  —  —  —  poisonous  substances, 162,  222. 
—  —  prickles,  221. 

spines,  221.  256.  260,  320,  331,* 

334. 

suspension,  320. 

teeth  of  leaf,  222,  334. 

texture,  223. 

thorns,  221,  260. 

—  cold,  353,  354. 

—  drying  by  calyx,  288. 

—  —  —  dispensing  with  leaves,  215,  331,* 

332,*  343.* 

enwrapping  leaves,  251,  261. 

hairy   coverings,    213,   333,  334,* 

335.* 

—  —  —  position  of  leaves,  217,  218.* 

—  —  —  reduction  of  leaf  -  surf  ace,   215, 

333,  342.* 
— —  number  of    stomata,  215, 

335,  336.* 
rolling  and  folding  of  leaf,  213, 

334. 

sinkingof  stomata,  215,  335,337.* 

storage  of  water,  331,*  334. 

thicker  cuticle,   333,  334,*   337,* 

338.* 

—  —  —  water-proof  substances,  214,  251. 

333.  334.* 
water-retaining  ^:ubstances,  216 

—  —  —  woody  coverings,  317. 

—  dust  by  hairs,  214. 

—  fire  by  bark,  256. 

—  fungi  by  bark,  256. 
callus.  263. 

—  water  by  callus,  263. 

hairs,  etc.,  214. 

wax,  214. 

of  plumule,  71,*  72.*  79.* 

—  root,  161.  162. 

Proteids.  decomposition  of.  38L 
energy  from,  173,  174. 
formation  of.  201.  253,  254, 


480 


INDEX 


Proteids,  in  animals,  171,  172,  176. 

—  Beans,  177. 

—  bran,  178. 

—  dietetics,  17G. 

—  eggs,  176,  177. 

—  flour,  177. 

—  friiits,  314. 

—  growing  region,  253-259. 

—  Peas,  177. 

—  seeds,  165,  166,  314,  437. 

—  Wheat,  177.  178. 

path  of,  in  stem,  227*  231,*  232,*  236,*  254- 
257. 

tests  for,  165,  166. 
Protoplasm,  65,*  66,  291.* 
Prune.     See  Plum. 
Prune,  French,  411,*  415,  416.* 

Giant,  410,  411. 

Stoneless,  415.  416,*  417. 

Sugar,  411.* 
Prunier,  sans  Noyau,  415,  416.* 
Pruning,  263,  346. 

correlation  in,  359. 

of  roots  to  increase  fruit -production,  319. 

self-,  261. 
Prunus.     See    Almond,    Apricot,    Cherry, 

Peach,  Plum  and  Prune. 
Ptyalin,  167. 
Puccinia.     See  Rust. 
Pumpkin,  fruit  of,  317. 

path  of  proteid  in,  254. 

tendrils  of,  272. 
Purslane,  protection  of,  from  animals,  223. 
Pusley.     See  Purslane. 
Putrefaction,  380. 
Pyrus.    See  Apple,  Pear. 

Quaker  Bonnets.     See  Houstonia. 
Quaker  Ladies.     See  Houstonia. 
Quartz,  105,  107. 
Quercus.     See  Oak. 

Quince,  absorption  of  water  by  seed  of,  7, 
28. 

branches  of,  twisted  in  layering,  314. 

seed-cover  of,  holds  water,  28. 

Radish,  absorption  of  water  by  seed  of,  7, 
28. 
germination  of,  47. 


Ra:\ish,  relation  of,  to  light,  265 

root-hairs  of,  100,*  101,*  121. 

seed-cover  of,  holds  water,  29. 
Ragweed,  protection  of,  against  animals, 

223. 
Rain  buries  seeds,  69. 

percolation  of,  in  soil,  111-118. 

puddles  soil,  129. 
Ranunculus.     See  Buttercup. 
Rape,  314. 

Raphanus.    See  Radish. 
Raspberry,  acid  in  fruit  of,  315. 

climbing  of,  270. 
Rattlesnake  Plantain.     See  Plantain,  Rat- 
tlesnake. 
Raw  Food.    See  Food,  Raw. 
Red  rays  cut  out  by  cupra  ammonia,  265. 
Regeneration  dependent  on  oxygen,  281,* 
282. 

in  stem,  257. 

of  root,  86. 

—  stem,  79.* 
Reproduction  by  seed,  291,*  292.* 

—  spores,  362,*  365,  393,  394,*  395,*  396.* 

397,*  398,*  399,*  401,  402,*  403,*  404.* 

—  vegetative  parts,  433. 
Reseda.    See  Mignonette. 

Resins  absent  from  water-plants,  339. 

protect  against  drying,  214.  334. 
Resistance  to  disease,  440. 
Respiration  defined,  175. 

increased  by  wounds,  388. 

measurement  of,  34,*  175. 

of  animals,  35,  176,  194. 

—  flowers,  287. 

—  fruits,  317. 

—  leaves,  194,  195. 

—  Moulds,  394. 

—  seeds,  33,  34.*  35,  b3.* 

—  Yeast,  390. 
Reversion,  420,  449,*  450. 
Rhamnus,  Rust  of,  405. 
Rheum.    See  Rhubarb. 
Rhizomes,  function  of,  277. 

propagation  by,  433. 

resemble  roots,  277. 

storage  of  food  in,  260. 
Rhizopus  nigricans,  391. 
Rhubarb,  bleaching  of,  346. 


INDEX 


481 


Rhubarb,  protection  of  root  of,  162. 
Ribes.    See  Currant. 
Rieinus.    See  Castor-bean. 
Riley  on  food  of  plant,  344. 
Rind,  function  of,  257. 

of  root,  120,*  121. 

of  stem,  224,*  225,*  232,*  233.  236.* 

starch  in,  258, 
Ring,  annual,  247. 

bast-226,  246. 

cambium— 246. 

woody,  226,  246. 
Ringing,  256,  257,  318, 
Ripening  of  fruits,  316. 

—  seeds,  314. 
River  water,  plant-food  in,  138. 
Rivers,  self-purification  of,  382,  383. 
Roberts,  on  fertilizers,  153. 
Robinia.    See  Locust. 
Rocks,  decomposition  of,  109,  144,  145. 
Roguing,  451. 
Rogues,  451. 
Rolling  of  leaf  protects  it  against  drj'ing, 

213,  334. 
Root,  aeration  of,  36,  37,*  38,  39,*  40,  103, 
119,*  120,*  124-126.  128,  130,  132. 

aerial,  275.* 

absorption  of  water  by,  88.  102,  103,  119,* 
120,*  121-123  * 

affected  by  heat,  332. 

salts,  124,  336. 

acid  excreted  by,  141-143,*  144,  145. 

anchors  plant  in  soil,  87.* 

behavior  of,  to  obbtacles,  99.* 

buds  formed  on,  249. 

care  of,  135,  136. 

climbing,  275.* 

contraction  of,  87. 

decomposes  rocks,  144,  145. 

depth  of  penetration  of,  134,  135. 

direction  of  growth  of,  influenced  by  air, 
89,  98,  135. 

centrifugal  force,  92.93,* 

94. 

■ food,  89,  98. 

gravity,  88,*  89.*  90,  91,* 

92,  93.*  94,  95,  98,*  99. 

heat,  89,  98. 

water.  89,  95,*  96.*  97, 98. 

EE 


Root,  effect  of  heat  on,  332. 

water  on  the  form  of,  341. 

etches  marble  and  plaster  of  Paris,  144. 

excretion  by,  141-143,*  144,  145. 

exploration  of  soil  by,  133-135. 

food  in,  122,  125,  260. 

force  of  growth  of,  81,  82,*  83,  84,*  85. 

fungi  on,  150. 

gives  off  carbonic  acid,  141-143,*  144. 

growing  region  of,  85,*  86. 

microscopic  structure  of,  120,*  121.  255. 

needs  air,  125. 

of  water-plants,  339. 

osmotic  action  of,  123,  124. 

path  of  water  in,  120,*  121. 

penetration  of  soil  by,  80.*  81.* 

propagation  by,  433. 

protection  of,  161,  162. 

proteids  in,  255. 

pruning  of,  136,  318. 

regeneration  of,  86. 

resemblance  of  rhizome  to,  277. 

selective  action  of,  161. 

shallow  vs.  deep,  87. 

storage  of  food  in  260. 

strengthening  fibers  of,  120,*  267,  268. 

sugar  in,  122. 

tip  of,  how  protected,  86. 

—  —  result  of  injury  to,  86. 

treatment  of,  to  promote  fruit  produc- 
tion, 342. 

tubercles  of,  49,*  384,  385. 
Root  cap,  86. 

Root-hairs,  absorb  water  by  osmosis,  121 
123,*  124,  242. 

effect  of  water  on  growth  of,  102. 

method  of  obtaining,  100,*  101.* 

of  radish,  100,*  101.* 

of  Wandering  Jew,  102.* 

relation  to  soil-particles,  119,  120,  121. 

turgidity  of.  123. 
Root-pressure,  243,*  244. 
Root-stock.     See  Rhizome. 
Rosa.     See  Rose. 
Rose,  calyx  of,  288. 

climbing  of,  270. 

protection  of,  against  animals,  221. 
Rose,  Moss,  origin  of,  by  bud  variation,, 420. 
Rose,  family,  cross-pollination  of,  303. 


482 


INDEX 


Rosette    form  as    protection  against   ani- 
mals, 223. 

—  of  alpine  plants,  357. 
Rotation  of  crops,  lGO-161,  407,  408. 
Roth,  on  forestry,  113,  245. 
Rubber  plant,  356. 

Rubus.     See  Blackberry,  Raspberry. 
Runoff,  113. 

Rushes,  protection  of,  against  animals,  223. 
Russian  Thistle,  dispersal  of  seeds  of,  322. 
Rust,  Black  Stem,  of  Grain,  401,  402,*  403,* 
404,*  405. 

Crown,  of  Oats,  40.'). 

Hollyhock,  406. 

Orange  Leaf,  of  Wheat,  405. 
Rye,  germination  of,  47. 

pepsin  absent  from,  172. 

Rust  of,  405. 

Smut  of,  400,  401. 

Saccharomyces.     See  Yeast. 

Sage,  cross-pollination  of,  305-306.* 

hairy  covering  of  leaf  of,  213. 

structure  of  flower  of,  306,*  307. 

brush,  protection  of  against  drying,  334.* 
St.  Louis,  water  supply  of,  382. 
Saleratus^l54. 

Salicylic  acid.     See  Acid,  Salicylic. 
Salix.     See  Willow. 
Saliva,  166,  167. 
Salt,  161. 

as  preservative,  385,  386. 

in  osmosis,  18. 

in  soil,  test  for,  158. 

sets  free  potash,  152. 
Salt  Bush  tolerates  alkali,  350. 
Salt  marshes,  absorption  difficult  in,  217. 
Saltpeter.     See  Potassium  nitrate. 

Chili.    See  Sodium  nitrate. 
Salts  in  soil,  13G-1G0. 

—  —  fixation  of,  by  soil,  145-147. 
form  crust,  127,  129. 

—  —  hinder  absorption,  18,  124,  217,  3:!f). 
needed  by  plant,  139,  140.* 

protect  plant  against  dryness,  216. 
Salvia.     See  Sage. 
Sambucus      See  Elder. 
Sand,  104,  147. 

bound  together  by  plants,  277. 


Sand,  freed  from  plant-food,  155,  156. 

microscopical  examination  of,  105. 

percolation  in,  113. 

plant-food  in,  105,  146. 

power  of,  to  lift  water,  118. 

properties  of,  105. 

water-holding  capacity  of,  132. 
Sandy  loam,  108. 

soil  for  cuttings,  262. 
Sap,   rise  of,  224-245,  2.59    (224,*  225,*  227.* 
231,*  232,*  234,*  236,*  237,*  238,*  240.* 
243*). 
Sap  wood,  244,  245. 
Saponification,  170,  171. 
Saprophj'tic  bacteria,  380. 
Saunders,  on  pruning,  264. 
Scabiosa.    See  Scabious. 
Scabious,  protection  of  pollen  of,  295. 
Scale  of  boilers,  151. 
Scale,  bud.    See  Bud  scale. 
Scar.    See  Hilum. 
Scarlet  avoided  by  bees,  298. 
Scarlet  fever.  329,  376. 
Scarlet  Runner,  144. 

absorption  of  water  by  seed  of,  12. 

germination  of,  59,  60.* 

getting  above  ground  of,  71. 

protection  of  tip  of  stem  of,  71,*  79. 

transpiration  of,  204. 

twining  of,  275. 
Scent.  See  Odor, 
von  Schrenk,  on  woods,  245. 

—  plant  diseases,  407. 

de  Schweinitz,  on  milk,  377. 

—  plant  diseases,  407. 
Scion,  248. 

Scirpus,  strengthening  fibers  of,  267.* 
Sclerenchyma.    See  Cell,  Sclerenchyma. 
Sea  water,  effect  on  germination  of,  18. 

renders  absorpti(Mi  difficult,  336. 
Seasoning  of  wood,  245. 
Secale.     See  Rye. 

Sedges,  protection  of,  against  animals,  222. 
Sedum.    See  Live-for-ever. 
Seeds,  air-dry,  contain  water,  7* 

air  needed  by,  30,*  31,  32,*  33,  36,  37,*  38. 
39,*  40. 

burial  of,  in  soil,  69,  70. 

carbon  dioxide  given  off  by,  6,  33,  34,*  35. 


INDEX 


483 


Seeds,  catdicle  of,  1,*  2,*  3.*  4.*  20,*  58.* 
chaflf  of,  holds  water,  29. 
diastase  in,  168,  1C9. 
dispersal  of,  by  animals,  323,*  324,*  325. 

—  —   —    mechanical   contrivances,   320, 

321.* 

water,  325. 

wind.  321,  322,*  323.* 

effect  of  extremes  of  temperature  on,  352. 

embrj'o,  288,  312. 

embryo  of.  1,*  2,*  3,*  4,*  20,*  56,*  58.* 

fat  in,  165,  437. 

ferments  in,  166-172. 

food  conveyed  to,  313,  314. 

—  in,  65,*  164-180,  437. 

—  transformed  in,  314. 

force  exerted  by  swelling  of,  48,  49,*  50, 

51,*  52,  53,*  54* 
germ  of.    See  Seeds   Embryo  of. 
germination  of,  1-86. 

affected  by  air,  5,*  6. 

— alkali  soils,  18. 

depth  of  planting,  38,  39,*  40,* 

41. 

drying,  47. 

heat,  5,*  6. 

light,  47. 

—  —  —  —  sea  water,  18. 

water,  4,  6. 

on  surface  of  soil,  69. 

quickness  of,  46. 

getting  above  ground  of,  71,*  72,*  73,*  74,* 
75,*  76,  77,*  79.* 

—  down  into  ground  of,  80,*  81,*  82,*  83, 

84,*  85,*  86.* 
heat  set  free  by,  35.  36.* 
hilum  of,  1,*  2.  10. 
immature,  germination  of,  43, 
lipase  in,  170. 
micropyle  of,  8,*  9. 
micr*^  scopic  structure  of,  65,*  66,  67,  177, 

178. 
needs  of,  4. 
oil  in,  165,  437. 

osmotic  action  of,  17,  18,  60,  63,  64,  67. 
path  of  water  in,  22,  23,*  24. 
penetration  of  soil  by,  8C,*  81.* 
pocket  around  caulicle  of,  20,*  58.* 
preservation  of,  7,  28,  45,  46,  385. 


Seeds,  proteid  in,  437. 

pepsin  in,  172. 

plumule  of,  1,*  2,*  3.*  4,*  20,*  58,*  59.* 

proteids  in,  105,  166. 

respiration  of,  33   34,*  35,  36.* 

resting  period  of,  43,  44. 

restored  by  ferments,  44. 

ripening  of,  314. 

starch  in,  05,*  164,  437. 

structure  of,  1,*  2,*  3,*  4.*  20,*  57,*  58,* 
59,*  65,*  180.* 

struggle  of,  for  existence,  312. 

sugar  in,  164.  165. 

small,  treatment  of,  41,  42. 

testing  of,  44,  45. 

tiansportation  of,  282. 

trypsin  in,  172. 

vitality  of,  44. 

water  in,  7,*  437. 

how  obtained,  6-30  (7,*  8,*  9,*  15,* 

19,*  20,*  21,*  22,*  23,*  26,*  27*). 

wrinkling  of,  in  water,  8.* 
Seed-beds,  screens  for,  41.* 

soil  for,  41. 
Seed-case,  3,*  4,*  288.*  289,*  290,  360. 
Seed-cover.  1,*  2,*  3,*  4,*  20,  21,  23,*  24. 

escape  from,  48,  49,*  50,  51*-54,*  55  *  57,* 
58,*  .59.*  60,*  61,*  62,*  63.* 

function  of.  47,  48. 

hinders  absorption  of  air,  30,*  31,  32. 

heat.  42,*  43. 

water,  8,*  9*-15,*  16*-19,*  20.  21,* 

22,*  23*-25. 

holds  water,  28,  29. 

openings  in,  8,*  9*-15,*  16*-19,*  20,  21," 
22  *  23*-25. 

osmosis  through,  16,*  17,*  18,  19,*  20. 

place  of  rupture  of,  54,  58. 
Seed-leaves,  1,*  2,*  3.*  4,*  178,  179,  180.* 

contrasted  with  foliage-leaves,  180-186- 

function  of,  163,*  164-179,  180.* 

number  of,  226. 
Seedlings.     See  Seed. 
Selection,  331,  433-453. 
Self-pollination,  301,  302. 
Self-sterility,  309. 
Senecio.     See  Ragweed. 
Septic  tank,  382. 
Serum,  171. 


484 


INDEX 


Service  berry,  hairy  covering  of  leaf  of,  213. 

Setchell,  acknowledgement  to,  x. 

Sewage,  purification  of,  381,  382. 

Shade  plants,  344. 

Shamel,  work  of,  434-439. 

Shells  as  fertilizer,  151. 

Shoot.     See  Stem. 

Sidewalks  exclude  air  from  roots.  126. 

Sieve  tubes,  227,*  231,*  232,*  236,*  254,  255. 

Silage,  387,  388. 

Silica,  145. 

Silt,  118. 

Silver  grain.     See  Medullary  rays. 

Silver  nitrate,  158. 

Simple  pits,  227,*  232.* 

Size,  increased  by  breeding,  410,  411,*  413,* 

416,*  422,  423.* 
Sleep  position  of  flowers,  294,  295. 

leaves,  218.* 

Smallpox,  379. 

Smut,  397-401. 

Smut  of  Corn,  397,  398,*  399,*  400,  440. 

Smut  of  Grain,  400-401. 

Smut,  Stinking,  400. 

Snapdragon,  flower  of,  opened  by  bees,  308. 

protection  of  pollen  by,  294. 
Snow  as  mulch,  117. 
Snyder,  on  fertilizers,  153. 

—  foods,  173,  178. 

Soap  for  soft?niug  bark,  248. 
Soda  for  softening  water,  151. 

in  soils,  test  for,  158. 
Soda-water  dissolves  marble,  etc.,  141. 
Sodium  chloride.     See  Salt. 

nitrate  as  fertilizer,  148,  153,  154. 

—  plant  selects  nitric  acid  from,  161. 
sulphate  in  soils,  158. 

—  test  for.  158. 

Soil,  absorption  from,  103-162. 
affects  the  distribution  of  plants,  351. 
action  of  rain  on,  111-113,  129. 
aeration  of,  126.  128. 
air  in,  36,  37.*  38.  39.*  40,  103,  119,*  120,* 

124-126.  128,  130,  132. 
alkali,  157-159. 
alluvial,  109. 

as  a  laboratory  for  preparation  of  plant- 
food,  146. 
as  a  sponge,  146. 


Soil  as  a  storehouse  of  plant-food,  146. 
burial  of  seeds  in,  69,  70. 
capillary  action  of,  116. 
chemical  action  in,  144-153. 
classified,  108. 
clayey, 106. 
color  of,  107,  108,  155. 
composition  of,  104,  105. 
contact  of,  with  seed,  21, 
crust  of,  116,  117,  125,  126,*  127,  129. 
drainage  of,  40. 
drift,  109. 

evaporation  from,  115. 
exploration  of,  by  roots,  133-135. 
formation  of,  109,  110. 
heart  of,  107. 
heat  absorbed  by,  43. 

—  retained  by,  43. 

humus  in.  104,  107,  132,  133,  145,  148,  351 

—  —  test  for,  155. 

injured  by  over-irrigation,  131. 

tilling  at  wrong  time,  129. 

lifts  water.  114. 
lime  supplied  to,  151. 

—  in.  test  for.  157. 
mechanical  analysis  of,  104. 
mellow,  107. 

mineral  substances  in.  136-160. 
nitrogen  supplied  to,  147-150. 

—  in,  test  for,  155. 
of  arid  regions,  146. 
phosphorus  supplied  to,  150. 

—  in.  test  for.  155.  156. 

physical  condition  of,  115,*  116,*  117,* 
119,*  120,*  124,  125,  126,*  127,*  128,* 
129-133,  384. 

potash  supplied  to,  152. 

plant  food  in,  136-160,  201. 

puddled.  125.  129. 

required  by  cuttings,  etc.,  108,  262.  263. 

salts  in,  136-160. 

sandy.  105. 

saturated,  118. 

sour,  sweetened  by  lime,  152. 

temperature  of,  43. 

tests  for,  155-160. 

texture  of.  See  Soil,  Physical  condition 
of. 

tilth  of.     See  Soil,  Physical  condition  of. 


INDEX 


485 


Soil,  transported,  109. 

washed  away  on  slopes,  113. 

water-holding  capacity  of,  132, 

water  of,  103. 

amount  suited  to  plants,  130, 131. 

how  absorbed,  111-113.  129. 

how  regulated,  132,  133. 

Soil-crumbs,  124-127*,  128*. 
Soil-floccules,  126,  127,*  128. 
Soil-mulch,  115,*  116.*  117.*  125,*  129,  133. 
Soil-particles,  119.*  120,*  128  * 
Solomon's  seal,  storage  of  food  in,  313. 
Sorrel,  wood.    See  Oxalis. 
Spanish   Bayonet,  protection  against  ani- 
mals, 221. 
Spatterdock,  337. 
Species,  origin  of,  441-453. 
Sphagnum.     See  Peat  Moss. 
Spines   protect  against   animals.   221,  256, 

260,  320.  331.* 
Spiral  tracheids,  227,*  229,  230,  231.* 
Spongy  tissue  of  leaf,  198,*  199,*  200. 
Spontaneous  generation,  365. 
Spores  of  bacteria,  362,*  305. 

—  Corn-Smut,  397,  398,*  399.* 

—  Mildew,  407.* 

—  Mould,  393,  394,*  395,*  396,*  397.* 

—  Rusts,  401,  402,*  403,*  404.* 
Sport.  See  Variation,  sudden. 
Spraying,  407. 

with  oil  injures  leaf,  215. 
Spring,  fat  changed  to  starch  in,  259. 

run  of  sap  in,  243,  259. 

sugar  changed  to  starch  in,  259. 
Spring-wood,  232,*  236,*  247. 
Springs,  formation  of,  117. 
Spruce,  protection  against  drying,  333. 

wood  of,  230. 
Squash,  cross-pollination  of,  302. 

effect  of  light  on,  184,*  185. 

fibrous  bundles  of,  224,*  226,  227.* 

fruit  of,  water  conveyed  to,  317. 

germination  of.  54,*  55,*  56,  81.* 

micropyle  of  8,*  9. 

path  of  proteid  in,  224,*  227,*  254-256. 

water  in,  224*-227,*  228-230. 

peg  of,  54*-56. 

root-cap  of,  86. 

root  pressure  of,  243. 


Squash,  sap  of,  forces  which  raise,  241. 

seed-cover  of,  holds  water,  29. 

seedlings  of,  184,*  185. 

sleep  position  of  seed-leaf  of,  218. 

stem  of,  microscopic  structure  of,  224,* 
226,  227,*  228,  229,  246. 

tendrils  of,  272. 

transpiration  of,  216. 
Squash  hybrids,  429. 
Squaw-vine.    See  Partridge-berry, 
Squirrels,  Ground,  bury  seeds,  69. 
Squirting   Cucumber.      See   Cucumber, 

Squirting. 
Stannard,  on  soil,  133. 
Starch,  absorption  of,  from  leaves,  183,  258. 

as  food,  164,  176. 

changed  to  fat,  253,  259. 

oil,  253,  314. 

sugar,  167-169.  258,  314,  391. 

conveyed  to  wood,  232,*  233. 

decomposition  of,  186,*  187. 

digestion  of,  166-169. 

disappears  in  darkness,  182,*  183. 

energy  from,  176,  196. 

formation  of,  dependent  on  air  supply. 
191.* 

chlorophyll,  185. 

light,  182. 

in  variegated  leaves,  185. 

leaves,    182-203,    (182,*   184,* 

186,*  191,*  192,*  193.*  198,*  199,*  201,* 
202*). 

stem,  278. 

fuel  value  of,  176,  196. 

in  buds.  253. 

—  chlorophyll  grains,  201,*  202.* 

—  cortex,  258. 

—  flour,  177. 

—  fruits,  314. 

—  growing  region,  253,  254. 

—  leaf-cells,  202.* 

—  medullary  rays  232,*  233.  258. 

—  potato,  328. 

—  rind,  258. 

—  seeds,  65,*  164,  314.  437. 

—  wheat,  177,  178. 

—  wood,  232,*  233,  257-259. 

path  of,   in  stem,  169,  254,  257,  258,  313, 
314. 


486 


INDEX 


Starch,  role  of,  in  proteid  formation,  253. 

test  for,  164. 

wandering  of,  169.  183,  253,  254,  313.  314. 
Starch-grains,  65,*  66,  201.*  202.*  367.* 
Starch-trees.  259. 
Steam  pressure  in  boilers.  74. 
Steapsin,  170. 
Steel  wire,  366. 

Stem,  air  supply  of,  278.  279,*  280,*  281.* 
282. 

annual  rings  of,  232.*  236.*  247,  262.* 

bark  of.  262,*  279. 

binding  of,  248. 

—  —  formation  of.  256. 

function  of,  256. 

protects  against  dryness.  333. 

stretching  of,  247. 

bast  of,  120,*  224,*  225,  227.*   231,*   232,* 
233,  236,*  254-257. 

behavior  of,  toward  obstacles.  79,*  80. 

bending  of,  to  increase  fruit  production, 
318,342. 

binding  of.  248. 

breaking,   to   increase   fruit   production, 
318,  342. 

buttresses  of,  247.  248. 

cambium  of,  227,*  232,*  236*  246-248. 

chlorophyll  of,  278. 

climbing,  270.  271,*  272,  273.  274.  275.* 

collenchyma  of,  268. 

correlation  in,  79    257,  359,  360. 

direction  of  growth  of,  affected  by  cen- 
trifugal force,  92,  93,*  94. 

gravity.  90,  91*.  92,  93*- 

95.  264. 

light.  261   264.  270. 

wind.  348.*  349.* 

effect  of  frost  o'n,  353. 

heat  on,  346. 

light  on,  220.  261.  346.  359. 

elasticity  of,  269. 

epidermis  of,  278. 

fat  in.  253,  259. 

fibrous  bundles  of.  224*.  225*.  226,  227*- 
231,*  2.32*-234,*  235,  236,*  246.  254-2.56. 

food  in.  169,   243.  250.  253,-260,  286.  287, 
313.  314. 

force  of  growth  of,  73,*  74.*  75.*  76.* 

function  of,  163-285. 


Stem,  girdling,  to  increase  fruit  production. 

257,  318. 
method  of  fixing  air-tight  in  stopper,  205.* 
microscopic  structure  of,  224,*  225*-227* 

232*-234*.  235.  236*.  246.  254-256.  267,* 

268,*  328,  333,*  334,*  335.* 
notching,  to  increase  fruit  production, 318. 
one-sided  development  of,  349,  350.'' 
path  of  air  in,  258,  278, 279,*  280,*  281,*  282. 
proteid  in.  227.  231.  232,*  236,*  254- 

257. 

starch  in,  169.  254,  313,  314. 

sugar  in.  259. 

water  in,  224*,  225.*  226,  227*-231.* 

232*-236,*  237,*  258. 
propagation  by.  433. 
proteids  in,  254-257. 
pruning  of.  261-264. 
regeneration  in,  257. 
—  of.  79  * 

regions  of  growth  of,  77,*  78. 
rigidity  of.  due  to  osmosis,  269. 
strengthening    tissues,    224,* 

231,*  232,*  236  *  267,*  268-270. 

tissue  tension,  268,  269. 

rind  of,  224,*  225.*  232,*  233.  236.*  257,  258. 

ringing  of,  244.  25",  318. 

self-pruning  of,  2C1. 

starch  in,  169,  253,  254,  260,  313.  3U. 

—formed  in,  278. 

storage  of  food  in,  253,  257-260,  286,  287. 

strains  of.  due  to  wind,  265. 

strength  of.  how  secured.  266.  267,*  268,* 

269.  270. 
strengthening  fibers  of,  224,*  231,*  2.32,* 

236,*  267,*  268. 

effect  of  water  on,  335.* 

struggle  among  branches  of.  261.  262. 

sugar  in.  243,  250.  254.  259. 

sunscald  of,  346. 

tendril-bearing,  270,  271,*  272,  273,*  274. 

tip  of,  how  protected,  79.* 

structure  of.  226,  250.*  251. 

twining,  275-277. 

twisting,  to  increase  fruit  production,  318, 

underground,  260.  277. 

weaving,  270. 

wood    of,    224*-227*.   228-231*.   232*-234.* 

235,  236*,  237*,  238*-240.* 


INDEX 


487 


Stem,  work  of.  163-285. 

See,  also,  Corm.  Rhizome  and  Tuber. 
Sterility,  self-,  309. 
Sterilizer,  363.* 
Stigma,  288-^-290,*  291,  292. 
Still.  137.*  138. 

Stinking  Smut  of  Wheat,  400-401. 
Stock,  in  grafting,  248. 

Stomata.  196-198.*  199,*  203*-206,*  207,  208.* 
209.* 

artificial.  210.*  211.* 

effect  of  light  on,  207-209,  345. 

function  of.  207.  208. 

mechanism  of.  208,*  209,*  210,*  211.* 

occur  principally  on  under  side  of  leaf, 
215. 

of  fruit,  317. 

—  water-plants,  339. 
protection  of,  against  dust,  214. 

—  —  —  water,  214. 

reduction  In    number  of,   as  protection 

against  drying,  215.  335,  3.36.* 
sunken,  as  protection  against  drying,  215, 
335,  337.* 
Stoneless  Plum-    See  Plum,  S'oneless. 
Stoneless  Prune.    See  Prune,  Stoneless. 
Stopper,  method  of  fixing  leaf  or  stem  air- 
tight in,  205.* 
Storage  of  food.    See  Food,  Storage  of. 

—  water.    See  Water,  Storage  of. 
Strains  in  beams,  265. 

—  stem,  265. 
Straw  as  mulch,  115. 

benefits  puddled  soils,  129. 
Strawberry,  effect  of  fertilization  on,  309. 

position  of  flower  of,  307. 

protection  of,  from  animals,  223. 
Strength  in  relation  to  material,  265.  266. 
Strengthening  fibers.  See  Cell,  Strengthen- 
ing. 
Structure,  Cellular.    See  Histology. 

microscopic.    See  Histologj'. 
Struggle  for  existence,  6,  46,  261,  262,  312, 

326,  330. 
String  Bean.    See  Bean,  String. 
Structure    determined     by    function,    179, 

186.* 
Style,  288.*  289,  290,* 
Sub-irrigation.  131. 


Sublimate,  corrosive,  as  disinfectant,  364. 

Subsoil,  107,  146. 

Succulents,  215. 

Sugar  as  preservative,  386. 

cane,  165. 

changed  to  starch,  259. 

coagulates  blood,  171. 

decomposition  of.  381. 

fermentation  of,  390. 

for  yeast  cultures,  389. 

formation  of,  201. 

in  fruits,  314,  315,  411. 

—  growing  region,  253,  254. 

—  osmosis  expei'iments,  16,*  17,  18,  19.* 

—  roots,  122. 

—  stems,  243,  250,  253,  254,  259. 

—  seeds, 104, 165. 

—  proteid  test,  166,  178. 

—  stigma,  292. 

produced  from  starch,  167-169,  258,  259, 

bl4,  391. 
role  of.  in  proteid  formation,  253,  254. 
test  for,  164,  165. 
travels  in  cortex,  254,  257. 

—  —  wood  in  spring,  259. 
Sugar  Beet.    See  Beet,  Sugar. 
Sugar  Cane.    See  Cane,  Sugar. 
Sugar  Corn.    See  Corn,  Sugar. 
Sugar  Maple.    See  Maple,  Sugar. 
Sugar  Prune.    See  Prune,  Sugar. 
Sulphate  of  ammonium.     See  Ammonium 

sulphate. 
Sulphate  of  lime.    See  Lime  sulphate. 
Sulphate  of  sodium.   See  Sodium  sulphate. 
Sulphur  as  disinfectant.  364. 

as  remedy  for  plant  diseases,  407. 

in  proteid  formation,  253. 

needed  by  plants.  139,  140.* 
Sulphuric  acid.     See  Acid,  Sulphuric 
Sundew  loves  sour  humus,  351. 

pepsin  in,  172. 
Sunflower,  cross-pollination  of-  '^O-l 

flowers  of,  298. 

effect  of  light  on,  298 

germination  of,  81. 

rise  of  sap  in,  241. 

root  cap  of,  86. 

root  pressure  of,  243. 

seed  of,  3.* 


488 


INDEX 


Sunflower,  seed  of,  resting  period  of,  44. 

seed-leaf  of,  sleep  position  of,  218, 

stem  of,  224,  269. 
Sunlight,     See  Light. 
Sunscald,  346. 

Superphosphate,  139,  150,  153,  154. 
Surface  crust.     See  Soil,  Crust  of. 
Surface  mulch.    See  Soil  mulch. 
Sweet  Pea.     See  Pea,  Sweet. 
Sweet  Potato.     See  Potato,  Sweet. 
Swingle,  on  Date  Palm,  294. 

—  on  Fig.  310. 

—  Smuts,  400. 

—  variation  due  to  environment,  421. 
Switch  Plants.  215,  331,  332,*  343.* 
Synergidae.  291.* 

Synclines,  111. 
Syringa.    See  Lilac. 

Taft,  on  soil,  133. 

Tar  excludes  air  from  stems,  281. 
Tarweed,  dispersal  of  seeds  of,  324. 
Teleutospores,  402.* 
Temperature.     See  Heat. 
Tendrils,  270.  271,*  272,  273,*  274. 
Terraces,  experimental  formation  of.  111. 
Texture  of  soil.    See  Soil.  Physical  condi- 
tion of. 
Thigmotropism.  272.  273.  274. 
Thinning  of  fruit.  312. 
Thistle,  dispersal  of  seeds  of,  321,  322. 

protection  of,  against  animals,  221. 
Thorn  apple,  protection  against  animals, 

222,  320. 
Thorns  protect  against  animals,  221. 
Thyme,  visited  by  bees,  299. 
Thymus.     See  Thyme. 
Tilia.     See  Linden. 

Tillage.     See  Soil,  Physical  condition  of. 
Tilletia.    See  Smut,  Stinking. 
Timothy,  flower  of.  280. 
Tilth.    See  Soil,  Physical  condition  of. 
Tissue.    See  Cell  and  Histology. 
Tobacco  crossed  with  Petunia,  432. 

fermentation  of,  388. 
Tomatoes,  canning  of,  386. 

immature  seeds  of,  germinate,  43. 

improvement  of,  by  breeding,  409. 
Touch-me-not.     See  Jewelweed. 


Toxins,  378,  379. 

TracheTd,  227,*  229,  230,  231.*  233,  234  *  235, 

236.* 
Tradescantia.     See  Wandering  Jew. 
Transpiration.  203* -205.*  206* -208.*  209,* 
210,*2ll*-218,*3]7.  328. 

affected  by  enwrapping  leaves.  251.  261. 

hairy  coverings.  213.  b33.  334.*  335.* 

light.  206.*  207. 

position  of  leaves,  217,  218.* 

reduction  of  leaf-surface,  215,  331.* 

332.*  333,  342,*  343.* 

— in  number  of  stomata,  215,  335. 

336.* 

rolling  and  folding  of  leaf,  213, 334. 

sinking  of  stomata,  215,  335,  337.* 

thicker  cuticle,  333.  334,*  337,*  338.* 

water -proof  substances,  214,  251. 

333,  334.* 

water-retaining  substances,  216. 

wind.  208.  348. 

woody  coverings,  317. 

Transplanting,  135,  136,  220,  359. 
Trees,  buds  on  roots  of,  249. 

effect  of  flooding  on,  125. 

frost  on,  352,  353. 

heat  on.  346. 

light  on,  220,  261,  346,  359. 

fat,  259. 

pruning  of,  263,  264. 

roots  of.  87.  125.  136. 

—  —  fungi  on,  150. 

seed  of,  how  preserved,  46. 

self-pruning  of,  261. 

starch,  259. 

struggle  among  branches  of,  261,  262. 

sunscald  of,  346. 

transplanting  of,  133,  220,  359. 

treatment  of,  to  increase  fruit  produc- 
tion, 318.  319,  342. 

See.  also.  Forest  and  Stem. 
Tree  of  Heaven.     See  Ailanthus. 
Triticum.     See  Wheat. 
Tropaeolum.    See  Nasturtium. 
Trypsin,  171,  172. 
Tuber,  propagation  by,  433. 

stem  nature  of,  260. 
Tubercle  bacteria,  149,  384,  385. 
Tuberculosis,  366,  376,  380. 


INDEX 


489 


Tulip,  opening  and  closing  of  flowers  of,  296. 

pollen  of.  293. 
Tulip  Tree,  protection  of,  against  dryness, 
213. 

transpiration  of,  204. 
Tumble  weeds.  322. 
Tourney,  on  forests,  113. 
Turgidity,  123,  124,  209,  269. 
Turnip,  storage  of  food  in,  260,  313. 
Tuttle,  acknowledgement  to,  x. 
Twinberry.     See  Partridge-berry. 
Twining  plants,  275,  276.  277. 
Twisting  to  increase  fruit  production,  318, 

319. 
Type,  420,  434,  450. 
Typhoid  fever,  371,  376,  379,  380. 

Ulex.    See  Gorse. 
Ulmus.    See  Elm. 
Uredospores,  402.* 
Urtica     See  Nettle. 
Urine,  48. 

U.  S.  Biological  Survey,  356. 
laboratory  for  plant-breeding,  441, 
Dept.  of  Agriculture,  publications  of,  113, 
129,  133,  153,  160,  178,  222,  245,  264,  294. 
310,  349,  354,  377.  384,  400,  407,  421, 433, 
434,  441. 

soil  surveys  of,  351. 

forests  of,  356. 
Ustilago.    See  Smut. 

Vaccination,  379. 
Variation,  bud,  420. 

cause  of,  421,  450. 

curve  of.  417,  418,*  419.* 

due  to  crossing,  422,  424.*  426,*  427*-429,* 
430,  434. 

environment,  326-360. 

fluctuating,   417.  418,*  419*-421,  442,  443, 
448.*  449,  450. 

lack  of,  in  vegetative  propagation,  433. 

production  of,  421. 

sudden,  420.  421.  442,'  443-445,*  446,*  447*- 
449,*  450-453.       • 

suppression  of,  433-434. 
Varnish,  absent  from  water-plants,  339. 

protects  against  drying,  214,  333,  334. 
Vegetable  matter.     See  Humus. 


Veins  of  animals,  176. 

—  leaf,  225. 
Verbascum.     See  Mullein. 

Vernation  as  protection  against  drying,  213. 
Vicia.     See  Horse  Bean. 
Vinca,  leaf  arrangement  of,  220,*  221.* 
Vinegar  as  preservative,  386. 

manufacture  of,  387. 
Viola.    See  Violet. 
Violet,  dispersal  of  seeds  of,  321. 

protection  of  pollen  of,  294. 

preferred  by  bees,  298. 
Violet  rays  cut  out  potassium  bichromate 

265. 
Virginia  Creeper  attracts  insects,  299. 

tendrils  of,  274. 
Vitis.  See  Grape. 
deVries,  acknowledgement  to,  x.  409. 

on  origin  of  species,  442-453. 

Waite,  on  plant  diseases,  407. 
Walnut,  cross-pollination  of,  302. 

germination  of.  59. 

leaf-scar  of,  212. 

seed  of,  path  of  water  in,  23,*  24. 

structure  of,  3,  23,*  24,59. 

seed-cover  of,  escape  from,  54. 

—  —  holds  water,  29. 

openings  in,  8,*  9.  23,*  29. 

Wandering  Jew,  102,*  138.  139.  140.* 

growth  of,  at  nodes,  250. 

root  cap  of,   86. 

root-hairs  of,  102.* 

roots  of,  102.* 

stomata  of,  196. 

supplies  carbon  dioxide  to  aquaria,  285, 
Ward,  on  plant  diseases,  407. 
Wasp,  power  of  scent  of,  300. 

vision  of,  300. 

Water,  absorption  of,  by  root,  88,  102,  103, 
119,*  120*-123.*  332.* 

seeds,  6,   7,*  8,*  9*-15,*  16-19.* 

20,*  21,*  22,*  23.*  26.*  27.* 

wood.  68. 

affected  by  heat,  332. 

force  required  for,  121-123.*  124. 

hindered  by  dissolved  salts,  etc.,  18, 

124.  217.  336, 

seed-covers,  8-26. 


490 


INDEX 


Water,  action  of,  on  soil,  109-114,*  115*-119,* 
120,*  129-133. 

amount  of,  in  air-dry  seed,  7.* 

• soil  needed  by  plants,  130,  131. 

wood,  24b. 

needed  for  germination,  25,  26. 

as  component  of  starch,  186. 

bacteria  of,  368. 

buries  seeds,  69. 

capillary,  113. 

decreasing,  promotes  fruit  production, 
319. 

distillation  of,  137.* 

distributes  seeds,  325. 

eflfect  of,  on  direction  of  growth  of  roots, 
89,  95,*  96,' 97,  98. 

form   of   plant.   326.   327,*   328,* 

329.*  .'530,  3."}1.*  332.*  333,*  334,*  335.* 
3.36.*  337,*  338,*  339,*  340,*  341,  342,* 
343.* 

growth.  116,*  117.  252. 

energy  required  to  raise,  in  stem,  239, 
210*-243.* 

evaporation  of,  from  leaves.  See  Trans- 
piration. 

soil,  115. 

filtration  of,  372. 

free,  113. 

haid,  151. 

hygroscopic,  113. 

injurious  in  stomata,  214, 

in  seeds  7* 

in  soil.  103,  111-135. 

how  regulated,  132,  133. 

formation  of,  lJ9. 

lack  of,  effect  on  fruit  of,  342. 

plant  of.  88,  211-217,  326,  327,* 

328.*  .329*-331,*  3.12,*  333.*  3.34,*  335,* 
336.*  3.J7.*  338,*  339,*  340*-342,*  343.* 

needed  by  fruit,  316,  317. 

pl.ant.  135,  211,  326. 

seed,  46. 

of  ponds  and  rivers,  plant-food  in,  138. 

path  of,  in  root,  120,*  121. 

seed,  8,*  22,  23,*  24. 

stem,  224,*  225,*  226,  227*-231,* 

232'-236,*237,*244,  258. 

percolation  of.  in  soil,  111-114,*  11.5-118. 

problem  of  obtaining,  6. 


Water,  protection  against,  by  callus,  263. 

hairs,  214. 

w.ix.  214. 

purification  of,  382. 

rate  of  travel  through  wood  of,  238,*  2.39 

rise  of,  in  soil,  114,  115. 

role  of,  in  starch  formation,  187,  193,  202. 

sea,  18.  124,  217,  336. 

storage  of.  in  plants.  331,*  334. 
Water-bath,  67. 

Buttercup,  338,  339.* 

culture,  140.* 

glass,  387. 

hyacinth,  340. 

lily.  337.  339. 

—  closing  of  flower  of,  295. 

—  protection  of  pollen  of,  295. 
Plantain,  342. 

plants,  characteristics  of,  .337,*  338,*  339,* 

340*-342. 
polygonum,  335,*  .336,*  340.* 
reservoirs  in  plants,  216. 
roots,  341. 
table,  118,  135. 
vapor,  effect  of,  on  opening  and  closing  of 

flower,  296. 
plant,  341. 

—  mfthod  of  keeping  air  saturated  with, 

26,*  27.* 

wheel,  93.* 
Wax,  absent  from  water-plants,  339. 

protects  against  drying,  214,  333,  334.* 

water,  214. 

Weather,  effect  of,  on  growth,  252 
Weaving  plants,  270. 
Webber,  on  fertilizers,  153. 

—  plant-breeding,  433,  441. 

—  pruning,  264. 

—  variation  due  to  environment,  421. 
Weed,  on  pollination,  407. 

Weeds,  destroyed  by  crop-rotation,  ICU. 

harbor  disease,  407. 
Weeping  Willow.     See  Willow,  Weeping. 
Wells,  whistling,  125. 
Wheat,  130.  138,  155. 

early,  how  secured,  355. 

germination  of,  47,  81. 

immature  seeds  of,  43. 

microscopical  examination  of,  177, 178. 


INDEX 


491 


Wheat,  proteid  in,  177. 

rust  of,  401,  402,*  403,*  404.*  405. 

starch  in.  177. 

stinking  smut  of,  400,  401. 

smut  of,  400,  401. 

stigma  of,  292. 

strength  of  stalk  of,  267. 

structure  of  grain  of,  178. 
Whistling  wells,  125. 
White,  acknowledgement  to,  x. 
White  Poplar.     See  Poplar,  White. 
Whiting.     See  Lime  carbonate. 
Whitney,  on  soils,  129. 
Wickson,  on  plant-bi-eeding,  441. 
Wild  Mustard.     See  Mustard.  Wild. 
Wild  Oat.    See  Oat,  Wild. 
Wiley,  on  bacteria.  384. 

on  soils,  153. 
Williams,  on  flour,  178. 
Willow,  cross-pollination  of,  302. 

cuttings  of,  need  air,  281,*  282. 

in  northern  latitudes,  356. 

pollen  of,  292. 

regeneration  in,  257. 

roots  of,  126. 

starch  in,  259. 

supplies  carbon  dioxide  to  aquaria,  285. 

transpiration  of,  204. 
Willow,  Weeping,  effect  of  light  on,  346. 
Willow  Herb,  dispersal  of  seids  of,  323. 
Wilted  plants,  treatment  of,  212. 
Wind  buries  seeds,  69. 

carries  pollen,  289,  300,  301. 

causes  strains,  265. 

disperses  seeds,  321-322. 

effect  of,  on  fruit,  319. 

leaf,  345. 

plant,  348,*  349,*  350.* 

transpiration,  208,  348. 

loosens  bark,  248. 
Witch  Hazel.    See  Hazel,  Witch. 
Witches'  Brooms,  359. 

Wood.  120,*  121.  198,*  199,*  224*-227.*  228- 
231,*  232*-234,*  235.  236*-237.  238*- 
240,*  341. 

absorbs  moisture  from  the  air.  68. 

annual  rings  of,  247. 

decomposition  ;f,  381. 

effect  of  water  su.jply  on.  335.*  340. 


Wood,  energy  needed  to  raise  sap  in.  239, 
210,*  241.  242.  243.* 

fall.  232,*  236,*  247. 

force  of  swelling,  68. 

heart  of,  214,  245. 

injection  of,  237. 

preservation  of.  245. 

rate  of  conduction  of  sap  in.  238.*  239. 

resistance  of,  to  weather,  245. 

sap,  214,  245. 

seasoning  of,  245. 

sectioning  of,  230. 

spring,  232,*  230.  217. 

shrinking  of,  245. 

starch  in,  257-259. 

sugar  travels  in,  in  spring,  259. 

swelling  of.  68. 

usefulness  of,  215. 

water  in,  245. 
Wood  Anemone.    See  Anemone,  Wood. 
Wood-ashes  as  fertilizer,  152-154. 
Wood  cells,  method  of  isolating,  235. 
Woodchucks  bury  seeds,  69. 
Wood  Sorrel.    See  Oxalis. 
Woodlands  remain  in  good  tilth,  129. 
Woo  ly  fiber,  deficiency  of,  in  water-plants 
339, 

ring,  formation  of,  226.  246. 

texture  protects  against  animals,  223. 
Woods,  on  fertilizers,  153. 

—  flour,  173,  178. 

—  food  of  plant.  349„ 

—  plant  diseases,  407. 

—  pruning,  264. 

—  soil,  129. 

Woolly  coverings.  See  Hairs. 
Wormwood,  protection  of,  against  animals 
2*^2 

drying.  213,  333.  334.* 

Wounds,  319, 

cause  fever,  388. 

treatment  of,  171. 

Xanthium ,    See  Cockbur,  Clotbur. 
Xenia,  311. 

Yeast,  169.  389,  390.*  391. 

Yellow  not  liked  by  bees.  298-299. 

Yellow  fever.  380. 


492 


INDEX 


Yellow  Lupin.    See  Lupin,  Yellow. 
Yellow  Mustard.     See  Mustard,  Yellow. 
Yield  increased  by  breeding,  414,*  435-437. 
Yucca.     See  Spanish  Bayonet. 


Zea.    See  Com. 
Zinc,  161. 

affects  flora,  351. 
Zinnia,  cross-pollination  of,  304. 
Zygospores,  396.* 


BOTANY 

An  elementary  text  for  schools 
By   L.  H.  BAILEY 

Professor  of  Horticulture   in   Cornell    University 
With  over  500  illustrations.      Half  Leather.      i2mo.     Si. ID,  net 

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Experiment  Station,  Auburn,  Ala. 

THE    MACMILLAN    COMPANY 

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LESSONS  WITH    PLANTS 

Suggestions   for  seeing  and  interpreting 
some  of  the  common  forms  of  vegetation 

By   L.  H.  BAILEY 

Professor  of  Ho.ticulture   in   Cornell   University 

With   delineations   from    nature   by  W.    S.    HOLDSWORTH,   of  the 
Agricultural  College  of  Michigan 

Second   Edition-446  illustrations  — 491   pages 
Half  Leather.     l2mo.     Si. 10,  net 

"It  is  an  admirable  book,  and  cannot  fail  both  to  awaken  interest  in 
the  subject  and  to  serve  as  a  helpful  and  reliable  guide  to  young  stu- 
dents of  plant  life.  It  will,  I  think,  fill  an  important  place  in  secondary- 
schools,  and  comes  at  an  opportune  time  when  helps  of  this  kind  are 
needed  and  eagerly  sought."— Professor  V.  M.  Spalding,  University 
of  Michigan. 

"I  have  spent  some  time  in  most  delightful  examination  of  it,  and 
the  longer  I  look,  the  better  I  like  it.  I  find  it  not  only  full  of  interest, 
but  eminently  suggestive.  I  know  of  no  book  which  begins  to  do  so 
much  to  open  the  eyes  of  the  student  —  whether  pupil  or  teacher  —  to 
the  wealth  of  meaning  contained  in  simple  plant  forms.  Above  all  else, 
it  seems  to  be  full  of  suggestions  that  help  one  to  learn  the  language  of 
plants,  so  they  may  talk  to  him." — Darwin  L.  Bardwell,  Superinten- 
dent of  Schools,  Binghamton,  N.  Y. 


FIRST   LESSONS  WITH   PLANTS 

The  first  twenty  chapters  of  the  larger  work  described  above 

117  pages.     116  Illustrations.     Cloth,  l2mo.     40  cents. 

All  of  the  illustrations  of  the  original  appear  in  these  selected  chapters, 
which  are  in  no  way  abbreviated 

"A  remarkably  well-printed  and  illustrated  book,  extremely  original 
and  unusually  practical." — H.  W.  Foster,  South  Orange,  N.  J. 

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BOSTON  CHICAGO  SAN   FRANCISCO  ATLANTA 


WORKS   ON    BOTANY 

CAMPBELL.— The  Evolution  of  Plants.  By  Douglas  Houghton  Camp- 
bell, Ph.D.,  Professor  of  Botany  in  Leland  Stanford  University. 

Cloth,   l2mo.     Si. 25 

University  Text-Book  of  Botany.    By  Douglas  Houghton  Campbell, 
Ph.D.     With  many  illustrations.  Cloth,  8vo.    $4,  net 

GANONG. —  The  Teaching  Botanist.  A  manual  of  information  upon 
botanical  instruction,  together  with  outlines  and  directions  for  a 
comprehensive  elementary  course.  By  William  F.  Ganong,  Ph.D., 
Smith  College.  Cloth,   l2mo.    SI. 10,  net 

MacDOUGAL. —  The  Nature  and  Work  of  Plants:  An  introduction  to 
the  study  of  botany.  By  D.  T.  MacDougal,  Director  of  the  Labora- 
tories, New  York  Botanical  Gardens.  Cloth,  l2mo.    80  cents,  net 

SETCHELL.. — Laboratory  Practice  for  Beginners  in  Botany.  By  William 
A.  Setchell,  Ph.D.,  Professor  in  Botany  in  the  University  of  Cali- 
fornia. Cloth,  l2mo.    90  cents,  net 

STRASBURGER.— Handbook  of  Practical  Botany.  For  the  botanical 
laboratory  and  private  student.  By  Dr.  E.  Strasburger,  Professor 
of  Botany  in  the  University  of  Bonn.  Translated  and  edited  from 
the  German,  with  many  additional  notes,  by  W  Hillhouse,  M.A., 
F.L.S.,  Professor  of  Botany  in  the  University  of  Birmingham. 

Fifth    edition,    rewritten  and    enlarged,  with  over  150  original 
illustrations.  Cloth,  Svo.    S2.60,  net 

STRASBURGER,  NOLL,  SCHENCK,  and  SCHIMPER.— A  Text-Book 
of  Botany.  By  Edward  Strasburger,  Fritz  Noll,  Heinrich 
Schenck,  and  A.  F.  W.  Schimper.  Translated  by  H.  C.  Porter, 
Assistant  Instructor  of  Botany,  University  of  Pennsylvania.  With 
594  illustrations,  in  part  colored.  Cloth,  Svo.    S4.50,  net 

VINES.— A  Students'  Text-Book  of  Botany.  By  S.  H.  Vines,  Professor 
of  Botany  in  the  University  of  Oxford.     With  many  illustrations. 

Cloth,  Svo.     S3.76,  net 

An  Elementary  Text-Book  of  Botany.     With  397  illustrations. 

Cloth,  Svo.     S2.25,  net 

THE   MACMILLAN   COMPANY 

64-66  FIFTH   AVENUE,   NEW    YORK 
BOSTON  CHICAGO  SAN  FRANCISCO  ATLANTA 


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